Bring back the toolbar shadow

Closes#477
See merge request !431
Care for lint errors
No more general disabling of abortOnError
Resolved all *errors* beside language ones MissingTranslation & ImpliedQuantity
Issue context: #567
See merge request !274
Make it clearer who will be introduced
Show contact names under avatars before sending introduction to make it clearer who will be introduced.

Closes#356
See merge request !242
Set focus mode properly when scanning QR codes
This simple fix contributed by @m8r-v9bo74 fixed the issue on my Xperia
Pro that could never focus on the QR code before. Focusing and scanning
still works on my other test devices.
Closes#346
See merge request !243
Improve Account Setup Screen
* Explain what "account creation" means on first run (#151)
* Use hints instead of dedicated text views
* Move password strength meter up into the user's view
* Always move user's view to current input field
* Improve "Forgot Password" dialog






Please note that the dialog button colors will be changed in !214 to the official design. Here they have the old colors.
Closes#151, #207
See merge request !229
Simple Empty State Messages
This MR implements very basic and simple empty state messages for the
current features.
This is how it looks (note that the contact add FAB will be removed soon):




Closes#327
See merge request !236
Update Timestamps Every Minute
Yes by using `notifyDataSetChanged()` I am invalidating everything, but view binding is very fast and the RecyclerView is smart about it. I could parse the dataset and use `notifyItemChanged()` only on the elements that matter, but this is not generic and a lot more code which is not necessarily faster. I suggest we go with my simple and generic approach for now and optimize when we actually notice a performance problem.
Closes#455
See merge request !238
Separate Date and Author Name in Forum Posts
This also fixes the issue there the trust indicator was shown at the top on some devices.

Closes#442
See merge request !227
Fix IdentityManager hooks
This commit makes sure that there is only one identity manager that is
initialized early enough so hooks can be added properly.
Closes#446
See merge request !225
Blog Client with Factories and Validator
This implements a simple initial blog client that covers the basic blog actions, but no deletion/removal of blogs, yet.
Classes for Blogs and Blog Post Headers have been introduced along with the associated factories.
A `BlogPostValidator` has been added that validates incoming blog posts.
Closes#402Closes#404
See merge request !212
New Trust Level Indicator Replaces The Stars
This implements a generic `TrustIndicatorView` with a `setTrustLevel()`
method which updates the drawable according to the `Author.State`.
It also removes unused files from the repo.
This is based on !212 and should only be merged after it.
Closes#78
See merge request !217
Blog Fragment in Navigation Drawer with Tabs
This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.
A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.
Please note that the header in the navigation drawer is just provisional. I am sure @Megalox can design a better one.


Closes#409
See merge request !210
122 threaded discussions
This branch contains the complete code for the nested forums (UI & back-end).
* This branch has an optional randomized set of dummy test data, uncomment one line in ForumActivity.java and then open up any forum.
See merge request !201