Parser & Checker (hopefully ;) corrected

- created new check_stm_ident() Method in Parser -> easier to check, if
	every ident in a stm is declared
- created proddiv(...)-Context-Check
- created assign(...)-Context-Check
- corrected wrong alternative-Nrs in ContextCheck-Methods
- added case for GREATER in: checkValidType(...)
- renamed Methods -> better seperation beween context-Methods and parsing-Methods

unsure: peek or pop in Methods (or does not matter)?:
	- context_cond_expr(...)
	- context_loop_expr(...)
	- context_assign(...)

Context-Check should be finished!! (if no Errors occur)