[FEATURE] simple search engine

SimpleSearchEngine follows the KISS principle and therefor tries not to introduce new datastructures - everything is boilerplate OpenMS code.
Currently, it is intended to help in perfomance measurements on OpenMS data structures and can be used to quickly test new ideas (e.g. scoring functions). On a QExactive dataset it performed similar to XTandem while beeing slower.
There is obviously a lot of room for speed improvements and suggestions are welcome. Changes introduced along with this pull request resulted from changes to `AASequence::operator==` or `operator<=`.
I can change this if wanted. At one point I thought its convinient to have all terminal modifed peptides at the "bottom". But I agree that the order you propose is more intuitive..