Fixing the initialization of the selected items in the multi-select for Knockout.js binding integration.  Currently a persisted binding value isn't being initialized correctly when using KO.  Instead the selectedOptions are only being set on during the update binding function or when the observableArray is changed.  With this fix, if the observableArray has initial values, they are selected as necessary.s

Conflicts:
	index-2-3.html
	index.html
	js/bootstrap-multiselect.js

** fix for #282: prevent crash when trying to select non-existant value **

prevent the "select all" from being created twice

Option groups support for the dataprovider method

Signed-off-by: Tyf0x <Tyf0x@users.noreply.github.com>

** Keyboard navigation fix: disabled elements are no longer selectable *...

** Removed the mirroring on the "Select All" option. **

Signed-off-by: Tyf0x <Tyf0x@users.noreply.github.com>

Signed-off-by: Tyf0x <Tyf0x@users.noreply.github.com>

Moving down the onChange callback

** Performance improvement ** - based on thorst #268 contribution.

adding namespace to fix keydown event.

Update bootstrap-multiselect.js

Fix multiple divider on rebuild().

Added Array forEach function for browsers that don't support EcmaScript5 (IE 8/9)

-> The deselectall function was deselecting all options regardless of their visibility. It now takes it into account.

-> Fixed a bug where disabled options where incorrectly selected using the 'select-all'
-> Changed the jQuery .not() selector in favor of the css native :not() to slightly improve performance

Divider was not removed on rebuild so each rebuild would add a new divider.

Moving down the onChange callback after this.updateSelectAll() allows to access the correct selected values during the callback.

Use the same format as Select2 : [{children: array (of options), [title: string]}]

Additionally :
- if no title is given, use the generic "Group n", with n as group index.
- for options if no label is given, use value as label

-> Now only filters the options to select if not all them have to be selected. This means to select all should be faster when there is no filter used.

-> improved performances and fixed the bug where the user couldn't deselect all in filtered mode
-> added the class multiselect-item to all plugin-specific items
-> fixed an incorrect CSS selector
Signed-off-by: Tyf0x <Tyf0x@users.noreply.github.com>