pfFilterPanel: Responsiveness needs to be addressed/overhauled

[dtaylor113]

Attempted to import Bootstrap's variables.less file and use @media(max-width: @screen-md-min) to address responsiveness layout in the pfFilterPanel.

A concern was: "if someone overrides bootstrap variables then includes a-pf less files, they will lose their overrides"

We need to figure out, in general, how to address responsiveness in angular-patternfly.
In addition, the pfFilterPanel needs to updated to handle resposiveness.

[dtaylor113]

Merging this issue with #600