Refactor files action of FilesController

Introduce service object RepositoryFile which
contains the logic of file and directory
retrieval on model level.

Introduce GitFile which contains logic of
file and directory retrieval on git/lib level.

Those classes separate the concerns of git/lib
and ontohub models way more.

Use InheritedResources for FilesController
and simplify files action (will be renamed later)
split history action off of files controller
fix remaining merge error
fix syntax error
code style
fix MethodMissing error
use correct method to disable the name field
disable editing of repo name in controller
code style: surround arguments by parens
Merge pull request #1029 from ontohub/1025-form_field_disabled

1025 form field is disabled
add test for the Repository scope 'pub'
outsource helper methods into HistoryHelper
rename HistoryEntries to HistoryEntriesPage
inherit from FakeRecord
documentation for HistoryEntriesPage
put attr_reader to the rop of the class
make compute_ref an instance method
un-protect methods that can't break anything
remove duplicate method
move attr_accessor to the top of the class