Add more tests to test_configuration

Dynamic configuration tests. Purpose: make sure that default configuration does 
not throw. Tests catch only very trivial problems (like missing imports after
refactoring)
Move some functions out of classes

No need to have static methods that are not supposed to be overridden and that 
do not benefit from `self' argument they do not receive
Removed underscore_to_camelcase

No need to bother both developers (that need to create class names compatible 
with file name, which is not obvious if not looking into main Powerline class) 
and computer (that needs to recompute class name each time) if it is possible to 
bother only developers (or only computer, but this contributes to higher startup 
times).

About not obvious: when you look into zsh_prompt.py and see only 
ZshPromptRenderer name you only think that powerline upstream is following 
strict code style. You don’t think there is a technical reason for such naming, 
like you don’t think there is technical reason for having blank lines. When you 
look into zsh_prompt.py and see `renderer = ZshPromptRenderer` it is obvious 
that there is technical reason for writing code this way because new variable is 
never used in the module itself.
Fix two flake8 errors
Add parameter to disable current and user directories shortening

Fixes #322
Fix keyword argument name
Make git.Repository.status() also return None

Fixes #326
Catch all urllib errors in urrlib_read()
Merge branch 'fix-urllib_read' into develop
Merge remote-tracking branch 'zyx-i/fix-322' into develop
Only use locally stored bzr branch nickname

Fixes #324 (slow vcs branch segment with bzr checkout)
Merge branch '324-fix-bzr-branch-name' into develop
Merge remote-tracking branch 'zyx-i/326-fix-None-handling' into develop
Make vim Visual Block mode orange in Solarized colourscheme.

This makes it consistent with the styles of the other visual modes.
Reference issue #147.
Merge branch 'fix-solarized-visual-block-color' into develop