Adds case insensitive filter

[steezeburger]

Most applications need case insensitive filtering. This PR adds that feature through the use of a contains_i input type.

{ Movie(filter: {title_contains_i: "river"}) { title } } 

TODO:

• write integration test

[textminer]

The addition of these filters would provide great benefit and with easiness to use

[michaeldgraham]

#608