Small fixes and Ivan updates
Changelog:

Plot models

Selecting terrain and saving it into models is now possible
Each Themed build has exactly one model assigned to it
Automatically given madel tool with instructions for ease

Plot protection

Fixed NullPointerException when a player interacted with air
Plot protection is now enabled only in world where current Themed Build is running

Terrain generation

Plots can now have different sizes
Plot signs are now wall signs attached to diamond blocks and are facing right direction
Plots are generated without using a model, model is generated when player claims a plot
Added sign with main ThemedBuild name
Gate with 'Closed' sign is generated when ThemedBuild ends

Known issues:

Claiming plots

If building on past plots is enabled, plot per player limit applies to all of them, not only those from current Themed Build