add loading class for mdo to style on customizer

BS3 commit dec00eeeafaa1272b8fc3754b8d134e8d358a6ed
fixes 6159

BS3 commit dbed9da77403337235acb652c3128ebc84672d60
refactor panels.less

BS3 commit 32369b2f789c4c93310cf4663c716cacd98c9de6
exclude bootstrap