Event-based message center communication

[daniele-athome]

The message center will live in the same process forever. Introducing a separate process for it means adding an overhead we don't actually need. Therefore, drop use of intents and broadcasts (even if local) and use a more human approach.

Using https://github.com/greenrobot/EventBus (almost) all commands and events will be converted to events. A few commands impact the internal working of the message center directly, and they will remain as intent-based commands:

• normal start
• ACTION_HOLD (can trigger connection; part of message center lifecycle)
• ACTION_RELEASE (part of message center lifecycle)
• ACTION_RESTART (can trigger connection)
• ACTION_TEST (can trigger connection)
• ACTION_PING (can trigger connection)
• ACTION_IDLE (sent from alarm)
• ACTION_PUSH_* (alters service state)

[codecov]

Codecov Report

Merging #1236 into master will increase coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1236      +/-   ##
=========================================
+ Coverage    0.52%   0.53%   +0.01%     
=========================================
  Files         288     330      +42     
  Lines       25311   24802     -509     
  Branches     3319    3254      -65     
=========================================
  Hits          133     133              
+ Misses      25165   24656     -509     
  Partials       13      13

Impacted Files	Coverage Δ
...k/service/msgcenter/group/KontalkGroupCommand.java	0% <ø> (ø)	⬆️
...service/msgcenter/MessageCenterPacketListener.java	0% <ø> (ø)	⬆️
...sgcenter/group/KontalkAddRemoveMembersCommand.java	0% <ø> (ø)	⬆️
...rc/main/java/org/kontalk/service/MediaService.java	0% <ø> (ø)	⬆️
...a/org/kontalk/upload/HTPPFileUploadConnection.java	0% <ø> (ø)	⬆️
...alk/service/msgcenter/RegisterKeyPairListener.java	0% <0%> (ø)	⬆️
...lk/service/msgcenter/event/RosterMatchRequest.java	0% <0%> (ø)
...p/src/main/java/org/kontalk/data/Conversation.java	0% <0%> (ø)	⬆️
...k/service/msgcenter/event/RosterStatusRequest.java	0% <0%> (ø)
...org/kontalk/service/msgcenter/MessageListener.java	0% <0%> (ø)	⬆️
... and 125 more

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