refactoring: move RubberBoard and Frame classes to separate files
PTHHBolt: added: parse_param, dimensions, repr
added locking bolt and removed nut; added min/max board angle; rubber board is now sliding;
added locking bolts for the other side of the rubber-board
added: cut in the vertical frame wood for the locking bolt of the other rubber-board side
fix: length of the locking bolt groove
use an U-profile instead of L-profiles in the bolt-guide
add back L-profile based bolt guide as an alternative