Documentation: Document old Code

[wurstbroteater]

In this project there are several method overloadings (#53 (comment), https://github.com/tthuem/VariantSync/pull/53#discussion_r565609049,https://github.com/tthuem/VariantSync/pull/53#discussion_r565604342, ...) or in general undocument usages of code parts.

This issue is considered as done if:

• The mentioned unclear usages (from here Fixed Compiler errors, updated to newest java version, updated travis, updated to newest featureIDE #53) are cleared and documented properly.