user-defined "import entity as" list

[Fennecai]

Is your feature request related to a problem? Please describe.
several entities specific to certain games do not currently import correctly, such as the portal 2 buttons (#151 )

Is your feature request related to a specific game? Please specify.
Mostly portal 2, but the feature would ideally be versatile enough to work for any game.

Describe the solution you'd like
in the addon preferences, there should be a box similar to the game directories box, which allows the user to define entity names, with the icon to the left representing import type (brush, modelname.)

the import-type is used to determine what the entity "is" in the vmf... for "brush," it would parse the brush like any other brush, but for "modelname" it would attempt to parse the modelname keyvalue of the entity and import that model.

for example, a brush entity and a model entity would be define by the user like this:
(brush) func_illusionary
(modelname) prop_floor_button

Additional context
a quick mockup of the above example

I believe this would be worth developing because then you wont need to go through every source engine game looking for incompatible entities to make new definitions of in your code. let the end user do the work for you on a case-by-case basis.