tests: Added test_unit_formatter.py
lib.formatter.units: Fixed _format() for ndigits=0

"not ndigits" for ndigits=0 is also be evaluated as true and the setting
wouldn't have been taken into account.
lib.formatter.units: Simplified unit definitions

Merged common code
lib.formatter.units: Used namedtuple for clarity
lib.formatter.units: Added DEFAULT_*_UNIT constants
lib.formatter.units: Converted constants to uppercase
lib.formatter.units: Explicitly convert value to float

Needed for some uses of the Decimal column type
templates/about: Use btn-group for social buttons
Merge pull request #91 from Turbo87/units

Units testing and simplification
Add Flask-DebugToolbar extension

This extension works quite a bit better than injecting get_debug_queries()
ourselves and gives even more information than that.
config: Removed unnecessary comma
config/testing: Make sure redirects are not intercepted
Airspace: update german airspace
Merge pull request #97 from Turbo87/config-typo

config: Removed unnecessary comma
config: Make DEBUG_TB_INTERCEPT_REDIRECTS = False the default
i18n: Updated Dutch translation
i18n: Updated Finnish translation
i18n: Updated Polish translation
i18n: Updated Russian translation
i18n: Updated French translation