Fix for null mimetypes in os_files alter #3513

Made sure to check if a mimetype was null before array merging it.  When they are empty, use the array we would have merged with.
Merge branch 'SCHOLAR-3.x' into 3513-os_files_null_merge

Conflicts:
	openscholar/modules/os/modules/os_files/os_files.module
sort extensions alphabetically
fields extensions.
more fields.
fix media gallery
Merge branch 'SCHOLAR-3.x' into 3513-os_files_null_merge

Conflicts:
	openscholar/modules/os/modules/os_files/os_files.module
Start work on the UX of event registration.
Add TODO.
Work on read-only mode.
Add custom message when site in read-only mode.
Fix comments.
Merge branch 'SCHOLAR-3.x' into 4365.
all file types allowed in all file fields besides image fields.
Add site/register path to be disabled in readonly mode.
Add update hook to modify variable value for enabled presets #4431
Adds multiple select/select2 to cp/build/taxonomy for bundle #4346
Add redirect paths to cp_admin_paths() #4433
Remove redirect code from cp_menu.module files #4433
Standardize @file documentation blocks