Improve GeneSetDb subsetting

[lianos]

Currently you have to pass in a logical vector as long as nrow(geneSets(gdb)) to filter out gene sets from a GeneSetDb.

I am imagining an NSE (and tidyselect-compatible) way to do this. For example,

From this:

gdb.all <- exampleGeneSetDb()
gs <- geneSets(gdb.all)
gdb <- gdb.all[gs$collection %in% c("c2", "c7")]]

To:

gdb <- gdb.all[collection %in% c("c2", "c7")]