Add random projections to dimensionality reduction class

[rchan26]

Add random projections as one of options for dimensionality reduction (into the DimReduce class).

• Add to "random_projection" as option to method argument
• Add description to docstrings for class
• Add further options for type of random projection ("gaussian", "sparse", ...)
• Return the fitted transform into .reducer attribute

[rchan26]

Implemented in develop branch: 5f3d75b