Add textbox/input for metapath and path query result limit

[vincerubinetti]

No description provided.

[dhimmel]

I know the path query results are ranked by "percent of DWPC". Let me double check how the limit will be applied to the metapath query. Note that limiting the metapath results is not necessary at this point because we will never have an unmanageable number of metapaths.

[dhimmel]

query-metapaths results are sorted as per:

https://github.com/greenelab/hetmech-backend/blob/38291721f64998ee1b5fe2d724191f7a5ba556ea/dj_hetmech_app/views.py#L81-L84

However, I don't think the backend supports a limit parameter AFAIK.