Implement parsing tests for standard library

[wegendt-bosch]

When the stdlib can't be loaded correctly that leads to all kind of funky behavior in the test suite. To make debugging the tests easier, we should try and parse/load all .x and .platform files in the stdlib plugin.

[wegendt-bosch]

We need a project org.eclipse.mita.library.stdlib.tests with basically two kind of tests:

1. Parse all .x and .platform files and check if they are valid => #51
2. Test Generators that come with standard library (String, Array, Printf, etc.) => #94