When we clear a list in onPause(), the proper behavior is that the empty state
message is shown, because the list is indeed empty.
However, we will reload the list content again in onResume(),
so the fix chosen in this commit is to force showing the progress bar
right after clearing the list.
Closes#576
This commit introduces an abstract `BaseContactListAdapter` which provides
most of the adapter logic. The original `ContactListAdapter` extends it to
show date and online status of the contacts.
The new `ContactChooserAdapter` which is used for introductions extends
the `ContactListAdapter` and adds logic for graying out contacts from
different identities than the currently used one.
A new `ContactSelectorAdapter` extends the `BaseContactListAdapter` and
allows to select multiple contacts. It offers a method to return a
collection of all selected `ContactId`s.
This commit also sneaks in an animation when the 'Share Forum' button
is clicked.
Closes#292
