feature: the statistic should respect the user mapping of the repository

Redmine already can map users to committers (applied to each changeset).
The statistic now respects this mapping by merging the data for all
committers which alias the same user.
removed the 1 year window for the commits_per_month statistic

the other graphs (commits_per_hours, commits_per_weekday, ...) don't have
such an window too
Merge branch 'feature-improved-statistic' of https://github.com/niosHD/redmine_git_hosting into niosHD-feature-improved-statistic
Rescue from RSpec error
Treat settings as string (like before)
Fix restore default settings from rake task
Fix https://github.com/jbox-web/redmine_git_hosting/issues/258
Fix default boolean value, failing tests
Fix settings on first migration
Refactor calls to sudo_pipe
Split GitoliteWrapper into modules
Remove cache on sudo tests
Refactor file creation via sudo into a single method
Fix no implicit conversion of Array into String
Add more tests
Fix redmine:plugins:migrate
Rescue from GitHosting exceptions in GitAdapter
Fix undefined method `config' for nil:NilClass, use accessors in Gitolite Wrappers
Run Gitolite repo creation tests independantly
Fix can't convert nil into String : default settings were not retrieved from init.rb file