Add possibility to change the order of plans

[akleber]

Currently plans are listed in the order they were created by default. This sorting can be changed but it is not persistent.
I personally would like to order the plans by the time they are configured to run.
The easiest would be if the default order can be adjusted manually for example through a "move up/down" action in the ... menu.
Currently I put the run time in the name and then can order A to Z but this is not persisted and kind of cumbersome.

[towfiqi]

@akleber Manual ordering is actually the hardest option as it requires a database schema change.

In v0.16.0, a few sorting and filtering improvements have been made:

• Its now possible to sort by run frequency.
• Sorting selection now persists.
• You can now filter plans by devices, plan type, destination storages and tags.

Hope this helps.