'Disable cache' option
Refactor. Model schema moved to assets_helper.py from db.py and queries.py.
Fix datetime issues with Safari. refs #85
Validate start and end datetime order. fixes #85
End time is the same as start time when adding new asset.
Disable cache option is hidden under Advanced section (only when asset type is image and it has URL).
Update Advanced section
Fix nocache toggle padding issue
Asset URLs are not fetched when an asset is or going to be disabled.
Allow aborting currently shown asset via SIGUSR1
Asset URLs are only fetched upon adding a new asset. viewer.py logs, if an asset appears to be offline. refs #91
More tests
Merge remote-tracking branch 'refs/remotes/origin/pr/92'
Don't show advanced section when editing uploaded asset.
Fix advanced section displaying
Fix modal max-height
Merge remote-tracking branch 'origin/pr/88'
Make active assets a drag&drop sortable list
Migration code for new column (ordinal)
New api endpoint at api/assets/order