Add xxhdpi check drawable for notifications

Fixes blurry mark as read icon on Android Wear. FREEBIE.
Merge pull request #1678 from veeti/check-icon

Add xxhdpi check drawable for notifications
use latest android number as recipient number

Fixes #791
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Update language translations.

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Bumping version to 2.1.0
Upgrade to latest Android gradle plugin

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Closes #1660
Add date to saved media filenames

Fixes #1689
Closes #1693
Add number of messages to the notification number attribute

Although not used by stock Android, many custom ROM's (and possibly OEM
versions?) have a setting to display the "number" count of a notification
overlayed on the status bar icon. Add support for this.

Closes #1637
Create a Curve25519 asymmetric master secret for users without.

Fixes #1701
Bumping version to 2.1.1
Upgrade to new GCM API.
disable passphrase creation on registration

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Closes #1726
new emoji drawer

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Closes #1746
Null check for cipher text to prevent NPE on decryption

Fixes #1703
Closes #1728
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Move default SMS and system import to "reminders"

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Closes #1730
Basic support for feature 520
Save drafts for recipients without an existing thread
Clear drafts when deleting conversation(s)

- Also don't save drafts when the thread was deleted from the
 ConversationActivity menu

otherwise the drafts stay in the database and will reappear when a thread
with the same threadId is created
Show Drafts in ConversationList
fix io on ui thread, parameter substitution