First version of S3 cloud files store support.
Merge branch 'master' into mw-filestore
mod_base: add GB to filesizeformat filter.
Better handling of errors.
Added error entry to filestore.
Fixes to race conditions.
Added download/upload all files options to admin ui.
docs: added stubs for new (filestore) modules, controllers and tpls.
docs: mod_zip is coming later...
docs: added first docs about controller_file.
Remove controller_file_readonly and controller_lib docs
mod_base: remove controller_lib, now replaced by controller_file
mod_base: merge 'acl' option from controller_file_readonly into controller_file.
core: set the base of relative root paths to the files directory of the site.
docs: small changes to controller_file doc
mod_filestore: fix retry after upload error.
mod_base: controller_file, is_authorized defaults should be true.
core: take the filestore-cache-entry's creation time as the modification time.
core: fix filename lookup and unique file generation for duplicating media items.
core: refactor file lookup from z_file_entry.erl to z_file_locate.erl.
Merge branch 'master' into mw-filestore

Conflicts:
	doc/ref/modules/mod_video.rst
	src/install/z_install.erl
	src/zotonic.app.src
Merge branch 'master' into mw-filestore
Merge branch 'master' into mw-filestore

Conflicts:
	modules/mod_base/controllers/controller_lib.erl
	src/install/z_install.erl
Merge branch 'master' into mw-filestore