Fix nonlocalized timestamp

On Android < 6 DateUtils picks up the system language to build strings, therefore the timestamps are shown in the wrong language when anything else than System default is used as language in Briar.

This MR fixes the following things:

• Update the system configuration on API < 23 so DateUtils picks up the right language
• Respect the deprecation of updateConfiguration where possible.
• Skips setting the locale if the os language is used
• Set the locale only once (on start).
• Hide languages using the Devanagari script on API 15
• Hides Asturian on API < 21 because it won't be picked up by Android.
• Fixes the foreground notification using the old language after account deletion.

I tested the changes (mostly) in the emulator an APIs 15,16, 21,23,28.

closes #1470