Hide multi-select actions not applicable to the current selection

[ByteHamster]

Checklist

• I have used the search function for OPEN issues to see if someone else has already submitted the same feature request.
• I have also used the search function for CLOSED issues to see if the feature was already implemented and is just waiting to be released, or if the feature was rejected.
• I will describe the problem with as much detail as possible.
• This request contains only one single feature, not a list of multiple (related) features.

App version

develop

Where did you get the app from

Google Play

Problem you may be having, or feature you want

When starting multi-select, AntennaPod shows both "mark as played" and "mark as unplayed" even if all selected episodes are unplayed. This looks a bit weird. Especially if we want to use that menu even for single-select at some point.

Suggested solution

Hide the actions that are not relevant to the current selection

Screenshots / Drawings / Technical details

Note that the current selection might be very large, especially with lazy loading. When "select all" or "select all below" was pressed (see SelectableAdapter.shouldSelectLazyLoadedItems), we should show all actions. Maybe even when a large number of items is selected, so that we don't need to loop over a huge number of items checking their attributes.