Reset @display when viewing drift history screen.

- Added change to reset @display when viewwing drift history screen to fix an issue where @display was still being set to vms/storages etc after clicking on links to relationships from host summary screen and then clicking on Drift History link from listnav on left side it was trying to render incorrect partial due to @display being set incorrectly. Drift History link from right side of the summary screen was working fine because going to summary screen resets @display back to "main"

- Added spec test to make sure @display gets reset by drift_history method.

https://bugzilla.redhat.com/show_bug.cgi?id=1123144
https://bugzilla.redhat.com/show_bug.cgi?id=1126085
replaced chart fieldsets with divs; added HRs where needed

https://bugzilla.redhat.com/show_bug.cgi?id=1124609
Converted image-based form buttons to Patternfly btn class buttons
Removed validation for group existence from controller

This validation is already being done by model, removed it from controller this was causing 2 flash messages on the screen.

https://bugzilla.redhat.com/show_bug.cgi?id=1092381
converted tabs to spaces, aligned hash rockets, adjusted formatting

Issue #1491
Merge pull request #322 from epwinchell/patternfly_formbuttons_1

Initial conversion of image-based form buttons to Patternfly btn class buttons
Merge pull request #338 from h-kataria/duplicate_flash_msg_on_group_add

Removed validation for group existence from controller
Merge pull request #335 from epwinchell/c_and_u_styling_fix

replaced chart fieldsets with divs; added HRs where needed
Merge pull request #329 from h-kataria/reset_display_instance_variable_when_viewing_drift_history

Reset @display when viewing drift history screen.