Media app + Gallery update

Since I have quite a lot of images in the media gallery of my website, I encountered some shortcomings while using the gallery and media app. Here, I list some of the most important missing features, feel free to add some in the comments.

For gallery / slider item manager and media app:

• Multiselection - select multiple files at once by using CTRL + clicking and SHIFT + clicking like in Windows Explorer
• DELETE-compability - use DELETE button to delete file
• Sellect all option - use CTRL+A to select all files in a folder

For gallery / slider item manager:

• Bulk editor - select multiple files and bulk edit the tags, image alt, description, ...

For gallery element:

• Alignment option - ability to center the images of a row if you have less than the max. images per row
• Mobile settings - use different settings in mobile version (e.g. max. images per row)

For media app:

• Folders - ability to easily organise your media in Folders
• File name editor