Feature: Send message via user dialog

[FelberMartin]

Problem Description

As described in #213 the "Send message" button in the user profile dialog has been postponed.

This PR closes #213

Changes

• Add button to User dialog
• Adapted navigation to properly handle navigating back from the "Send message" conversation to the previous chat
• Changes LocalVisibleMetisContextManager to being able to extract current metisContext, to avoid passing down the courseId all the time.

Steps for testing

• Go to any chat
• Click on a message
  • From yourself -> see that "Send message" button is not shown
  • From someone else, click on "Send message" -> navigated to DM chat (newly created in case it did not exist yet)
• Navigate back (via Android back button) -> previous chat is shown
• Click on a user mention in a post (or create a new one) -> see that navigation also works

[julian-wls]

When clicking on the user profile picture in the chat it works as expected.
The navigation works great, good work!

When clicking on the user profile picture in the ConversationMemberList the app crashes with the following stacktrace:

One more comment on the dialog:
I think it would be nice to stick to the new role badges from now on and use this design (see iOS app):

[FelberMartin]

When clicking on the user profile picture in the ConversationMemberList the app crashes with the following stacktrace:

Good catch, this is fixed now :D

I think it would be nice to stick to the new role badges from now on and use this design (see iOS app):

I created a follow-up issue for this as this change should then also affect the ConversationMembersList and bloat the scope of this PR: #289

[eylulnc]

Looking good!
Crash is fixed when clicking the image.
From yourself -> see that "Send message" button is not shown ✅
From someone else, click on "Send message" -> navigated to DM chat ✅
Navigate back -> previous chat is shown ✅
Click on a user mention in a post -> navigated to DM chat ✅

[julian-wls]

It's looking good now, no more crash!
Code also lgtm.