Respect ignoreCase flag in CommonGramsFilterFactory

[chenhh021]

Fix #780.

[paulirwin]

For posterity, this is a port of apache/lucene#188 although only part of that PR. I think this is a fairly reasonable change to make, as it does not change the public API surface and seems like it was clearly intended to function this way. I think we can include this in 4.8 unless @NightOwl888 disagrees. Adding to the beta 18 milestone for now.

[NightOwl888]

While normally I don't like to accept any future updates without getting the entire patch, there doesn't seem to be much benefit from the rest of the changes as they apply a AbstractWordsFileFilterFactory which doesn't yet exist. And since this fixes a bug, it seems appropriate.

There was one incorrectly translated line, that we should fix, though. See the inline comment.