Motivation

See #904; sometimes after a mod goes out of maintenance, a successor takes its place. It would be helpful if we could give users a cue that this has happened.

Changes

This is #1888 rebased onto current master, plus:

• Replace checkbox column
• Replaced by field added to mod info pane
• Replacements handled in change sets and installer
• Replaceable filter

For testing, I set up a fake relationship to replace KSP-AVC with ZeroMiniAVC:

Checking the box updates the change set to remove the replaced mod and install the replacement:

Not done:

• Right click menu option. I didn't think this fit well since we have a checkbox for it anyway.
• Netkan validation. This would be done in xKAN-meta_testing instead, e.g. Check that spec_version >= 1.26 for any_of xKAN-meta_testing#45
• Tests

Fixes #904.
Closes #1888.

Side fixes

• Reset the Update checkbox when clearing the change set (discovered because we need to do the same with the Replace checkbox)
• Centralize filter definitions in IsModInFilter rather than implementing them in multiple places
• Release status in mod info was often wrong because it wasn't updated when null, now it changes to N/A
• The mod list right click menu now looks better in dark themes