admin-ui: Clean up button stye

Basic button classes are:

* outline-btn: Transparent button with thin colored border
  and color font that get a thicker border on hover (default
  color is white)
* custom-btn: Colored button with white font that gets more
  opaque on hover
* line-btn: Total-black button with a white thick bottom border
  on hover
admin-ui: Hide 1st column in user's modals

Exception: The contact modal
Fix apyrgio/synnefo#135
admin-ui: Different active/hover style for menu
Merge branch 'feature-admin-design' into feature-admin
admin-ui: Filters clean up

Fix apyrgio/synnefo#157
Merge branch 'feature-admin-design' into feature-admin
admin-ui: Fix modals table & legend style
admin-ui: Change link-color and link-hover-color
Merge branch 'feature-admin-design' into feature-admin
admin-ui: Set the position of sidebar fixed on scroll

Fix apyrgio/synnefo#88
admin-ui: Update the design of toggle-selected btn
admin-ui: Add action handling
admin-ui: Minor style fixes for modals
admin-ui: Improve notifications