Move import/export operations into an independant class

- import and export are now two methods of importExportController
- "opml" has been removed from the title
Merge branch 'dev' into 163-export
New version to export articles + opml

It does not work yet! A lot of work has still to be done.
Next versions should fix TODOs

- OPML export works fine but can be improved
- a framework has been created for articles export
Merge remote-tracking branch 'origin/dev' into 163-export
Minz: remove one layer of ob_ (experimental)

https://github.com/marienfressinaud/FreshRSS/issues/303#issuecomment-38351311
https://github.com/marienfressinaud/FreshRSS/issues/163
* Remove Minz_Response (not needed anymore)
* Move Minz_Request::reseted to Minz_Dispatcher::reset()
Constant to enable PHP compression

https://github.com/marienfressinaud/FreshRSS/issues/303#issuecomment-38477994
Minz: remove url_rewriting

As suggested
https://github.com/marienfressinaud/FreshRSS/issues/163#issuecomment-38478669

At the same time, removes a bunch of (almost) dead code such as
Minz_Router (the few remaining lines being moved to Minz_FrontController
to avoid a class)

Contributes to https://github.com/marienfressinaud/FreshRSS/issues/303
Merge branch '163-export' into dev