trimModel: trim an expansive model to a more credible one, using...
In PriceLab/trenaSGM: trenaSGM: trena single gene model

trim an expansive model to a more credible one, using parameterized voting scheme

1	trimModel(tbl.model, tbl.reg, votesNeeded = 3, tf.keepers = c())

`tbl.model`	a data.frame, an expansive, unfiltered trena model data.frame, with perhaps > 200 tf rows
`tbl.reg`	a data.frame, included here only so that it can be returned, filtered to exclude binding sites for tfs which did not make it into the trimmed model
`votesNeeded,`	numeric, typically 2 or 3, at least this many votes, by any solver method, is required to keep
`tf.keepers,`	a character vector, keep these in the model no matter how well they performed. a tf in the model