Use contact ID rather than messaging group ID to identify conversation
We originally used the private messaging group ID to identify the private conversation, but now that the conversation includes messages from multiple clients it's more appropriate to use the contact ID.
This refactoring isn't urgent - I've had the branch lying around for a while, but I'm putting it up for review because #734 will touch some of the same code.
See merge request !386
Remove forum content type and change bodies to string
Also removes support for anonymous forum posts.
This MR depends on !360.
Closes#698, #681
See merge request !370
Implement UX for showing and answering private group invitations
As usual, this MR contains several logically separate commits that could be split out into smaller MRs if desired. It consists of two main parts:
* Showing open invitations in the list of private groups with a snackbar
* Showing invitations and responses in the private conversation
For both parts, the existing code was refactored to allow for a smooth implementation and to leave maintainable code behind.
Closes#707
See merge request !357
This way the forum and private group client do not need to keep track of
message timestamps themselves and do not need to interact with
post/message factories.
Null safety annotations
The @NotNullByDefault annotation marks all fields, methods and parameters in a class or package @NotNull, so Android Studio will warn if values that may be null are used. Please use this annotation for new classes, and specify @Nullable for any fields, methods and parameters that may be null.
Injected fields are initialised to null, so injected classes should use @MethodsNotNullByDefault and @ParametersNotNullByDefault, or specify @Nullable for injected fields.
See merge request !349
