Move langauge detection to separate module to be more reusable

Add option to disable vendored file exclusion from file search

Allways show all language stats for search

* Refactor code indexer

* fix test

* fix test

* refactor code indexer

* fix import

* improve code

* fix typo

* fix test and make code clean

* fix lint

* add global code search on explore

* fix bug when no anyone public repos

* change the icon

* fix typo and add UnitTypeCode check for login non-admin user

* fix ui description when no match

* Replace all ctx.Handle with ctx.ServerError or ctx.NotFound

* Change Handle(403) to NotFound, avoid using macaron's NotFound

Indexed search of repository contents (for default branch only)