Feature: Allow mark prioritization in-combat, while preserving markers on pre-combat units

[neotron]

Scenario: New group is pulled mid-combat (or patrol comes or what not). Want this group marked and prioritized.

Current behavior: You can mark, but prioritization doesn't take place to avoid changing pre-combat marks around.

Fix: Allow mark reprioritization on units marked while in-combat, while preserving pre-combat unit marks.