Add slash commands to exclude minimap buttons from the Collector

[Hippoom]

The minimap button Collector currently takes ownership of detected minimap buttons automatically. Some addon buttons do not behave well when collected, or users may simply prefer to keep certain buttons outside the Collector.

There is currently no simple user-facing way to release a specific button from the Collector and keep that preference after reload.

Expected behavior

Users should be able to:

• list known Collector buttons
• exclude a button from collection
• add a button back to the Collector
• reset all Collector exclusions

Excluded buttons should remain excluded after reload.

Actual behavior

Collector ownership is automatic, and users cannot persistently exclude individual minimap buttons.

Proposed fix

Add Collector slash commands under /dfrl collector:

/dfrl collector list
/dfrl collector del <ButtonName>
/dfrl collector add <ButtonName>
/dfrl collector reset

The implementation adds a persistent Collector.excluded list and updates Collector ownership behavior:

• del releases the button from Collector ownership and places it at a visible fallback position near the minimap
• add removes the exclusion and lets Collector manage the button again
• list shows known buttons and their collection/exclusion state
• reset clears all exclusions

This gives users a safe manual escape hatch for incompatible or preferred minimap buttons.