Update bootstrap version to 3.2.0

* NOTE: HTML and CSS are adjusted yet to the
  new bootstrap version.

* refs #17704
Bootstrap update: Fix navbar

* refs #17704
Bootstrap update: Fix buttons

* refs #17704
Bootstrap update: Remove obsolete images

* refs #17704
Bootstrap update: Replace glyphicons by font awesome icons

* refs #17704
Bootstrap update: Fix forms

* refs #17704
Bootstrap update: Fix modals

* refs #17704
Bootstrap update: Fix special leave popover in app form

* refs #17704
Bootstrap update: Fix table headers' position

* refs #17704
Bootstrap update: Remove bootstrap theme

* refs #17704
Bootstrap update: Fix login page

* refs #17704
Bootstrap update: Adjust navbar colors

* refs #17704
Replace logo in header

* refs #17704
Bootstrap update: Remove unsemantic grid css

* Instead of using grid system of unsemantic grid css,
  use the grid system of bootstrap instead.

* refs #17704