#14: moved content of Prop.hs into World.hs to avoid circular dependency
between module World and module Prop.
Deleted Prop.hs, there is no Prop module any more, everything from it is in the World module.
#14: first working implementation of conjugProp
it is a list of Strings instead of a String now but it's this should be changable easily
#14: commented out all the verbs we don't use across all three word collection files (Conjugationshs, Lexicon.hs, VerbRoot.hs)
#14: first complete, working implementation of conjugProp
#14: moved the isLeaf function into conjugProp since it is only used there
#14: added unit tests for connjugProp. Closes #14.
made sure all used verbs are uncommented in the verb collections and added the missing verbs as static files to the file heads which are used when generating the verb collections