Lipid2MD need to include option form manual selection of lipids

[MatteoLambrughi]

The user should have the option to manually select lipids to be included in the final membrane model. This is important for some design, for example to include choice of lipids based on literature knowledge etc. An example is that from lipidomics data it could happen that the class PG includes also the BMPs (since they are PG isomers and need specific lipidomic experiments to identify them) especially from data of lysosomes. Thus Lipid2MD for now automatically select a PG species when should select a BMP for having a model of lysosome.