WIP for review: Adding ShipManufacturer constants

## What this does
Introduces ship manufacturer constant, which are then used by the ship definitions, and gives warning if entered incorrectly when loading the ship models. Also lets faction scripts set weight of a manufacturers presence in said faction. There's no handling for default behaviour here yet. That is to come.


## Why
Instead of doing one giant pull request, I'm splitting this into many small ones, and this is (hopefully) the first in a series, to bring in faction specific repair prices and availability of ships in ship market. (as suggested on [dev-forum:post](http://pioneerspacesim.net/forum/viewtopic.php?p=2803#p2803) by @nozmajner)


## Review
I'm looking to get my a$$ handed to me, because I know this can be improved, so please point me in the right direction from here. I put the constants in `Polit.cpp`, feeling very dirty as I did so. Please grunt if they should be moved. I also had to convert the manufacturer constant to lowercase when using them on the ship textures, which feels a bit "ugly". I guess this aught to be in Lua but I was more confident on how to do it in c++, since we already have existing code for that. 

Last commit just adds some manufacturers to SolFed, and tests error message printout.

## next step
Will be to expose this to Lua. But that's another PR, if this isn't completely killed.