Add Support for Overlay Plugins

[Infernio]

Starfield introduces a new flag for plugins, which we've standardized on calling "Overlay". Current understanding is as follows:

• The flag's index is 0x200, where the ESL flag used to be (which is now 0x100).
• An overlay plugin cannot have the ESL flag set as well - if the game finds both, it ignores the Overlay flag.
• An overlay plugin cannot have new records (well, technically it can, but it really shouldn't - they get injected into the the first master in the plugin's master list, which is not a desirable situation, obviously).
• An overlay plugin does not take up a load order slot at all.
• An overlay plugin must have at least one master - if the game does not find a master, it ignores the Overlay flag.

This makes them ideal for conflict resolution patches, for obvious reasons.

Wrye Bash should:

• [x] Parse the flag correctly.
• [x] Allow loading an unlimited number of overlay plugins.
• [x] Remove the ESL flag when we write a plugin that has the Overlay flag.
• [x] Not mark overlay plugins as ESL-capable.
• [x] Display the number of active overlay plugins in the status bar.
• [x] Warn about plugins (in the Plugin Checker) that have the Overlay flag set but include new records.
• [x] Warn about plugins (again, in the Plugin Checker) that have the Overlay flag set but also have the ESL flag set.
• [x] Warn about plugins (you guessed it, in the Plugin Checker) that have the Overlay flag set but have no masters.
• [x] Allow creating Overlay plugins via New Plugin...
  • [x] Also, New Plugin... should disable the ESL checkbox if the Overlay checkbox is selected (and vice versa).
  • [x] And the Overlay checkbox should also get disabled if no masters are selected.
• [x] Show a new color (and mouseover text) for overlay plugins - plus one mixed with the ESM color (no need for mixed overlay and ESL, obviously).
• [x] Check for Overlay-capable plugins and highlight them (time to refactor that system for good).
• [x] Feature an option to Overlay-flag a plugin, similar to how we ESL-flag.

[LordNyriox]

@Infernio: I find it interesting that these 'overlay' plugins sound similar to the 'mergeable' patch plugins from older Bethesda games.

Once the Starfield plugin format has been fully decoded, perhaps you could implement the Starfield Bashed Patch as an 'overlay' plugin (instead of an ESL)?

[Infernio]

Potentially, but the BP can actually contain new records (GMSTs). Plus we already flag it as an ESL, so it's not going to take up a full slot anyways.

[Infernio]

We don't inject them anymore, not since 308. We create new GMST records for all games instead, because injecting records is actually quite dangerous and the only thing that used to stop us from creating new records was that there was simply no code in place to create new records in the BP. Once #312 (especially tweak pooling) paved the way for that, we switched to creating new records (and nuked some giant database files that were needed for the injection, which was nice as well).

Edit: see a5b8f9635e384519e931e1be0c3ddd1154b9bc00 (32 additions and 21,945 deletions). Also, it was 308, not 307, corrected.

[Infernio]

We may still do it, but we'll see how the BP shakes out for Starfield first (which will obviously have to wait until SF1Edit is reliable and maybe even until the CK is released).

[Infernio]

Alright, should be done. Note that none of it will work in Starfield yet (except for the new color for Overlay-flagged plugins), because canBash is False for Starfield right now, which disables everything to do with plugin manipulation.