first iteration of locking enemy data / readonly mode

[travisneids]

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[travisneids]

First attempt at a very dumbed down version of a read-only mode related to issue #67. Once enemy/route data is cleaned up we can hopefully add a reference to which pull an enemy belongs to in the DungeonToolsEnemyMixin:OnClick() function but as of right now there is no easy way to give DungeonEnemies objects context of which Pull it belongs to

[travisneids]

@srenauld thank you for the suggestions. I removed the setting from the addon DB and I also refactored some of the code to make it more scalable (ReadOnlyMode) as I'm sure there will be more than just locking the enemy's placements in future releases for Read Only mode.