Cache bust some frequently updated assets

[mitchray]

This uses the MD5 hash of a file to create a unique cached version, to avoid 'just clear your browser cache' issues

• Reference a cached version of asset if it exists, otherwise create cached version and reference it, or fallback to original file
• Added 'Clear Assets Cache' option to Ampache Debug page
• Change paths in CSS to be web root relative to account for different physical locations of original and cached CSS file

Not sure if I should also clear the asset cache during clean_catalog() just so its periodically cleared?

[codeclimate]

Code Climate has analyzed commit c4af2dd and detected 22 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Bug Risk	20
Security	1
Style	1

Note: there are 20 critical issues.

View more on Code Climate.

[lachlan-00]

could do it as part of the update function in AutoUpdate::update_files?

that would then clear it after an update

[mitchray]

Sweet, added!

[lachlan-00]

nice, worked a treat