Option groups support for the dataprovider method

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
prevent the "select all" from being created twice
** fix for #282: prevent crash when trying to select non-existant value **

Signed-off-by: Tyf0x <Tyf0x@users.noreply.github.com>
Fixed #322
allow onChange to trigger when calling `select` or `deselect` with one value
Merge pull request #281 from conradfr/master

Option groups support for the dataprovider method
Merge pull request #318 from shayh/master

prevent the "select all" from being created twice
Merge pull request #319 from Tyf0x/fix_#282

** fix for #282: prevent crash when trying to select non-existant value **
#301, additional documentation.
Merge branch 'master' of https://github.com/davidstutz/bootstrap-multiselect

Conflicts:
	index-2-3.html
	index.html
	js/bootstrap-multiselect.js
#329.
Update bootstrap-multiselect.js
Little correction to dataprovider.

There is a little correction to the method dataprovider, the parameters for the callback function are index, value.  Probably the problem is that in the forEach method of an array this two parameters are inverted.
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
Changing .less file
Merge pull request #346 from marcola/fix_#322

Fix #322
Merge pull request #343 from goncons/master

Little correction to dataprovider.
Merge pull request #341 from ellauty/master

Update bootstrap-multiselect.js
Merge pull request #345 from nnieslan/master

Knockout.js Binding: Fixing the initialization of the selected items in the multi-select
#347.