/*
A tool definition is an object with the following key/value parameters:
action: [function(deferred, restoreSelection)]
a function that is executed on clicking on the button - this will allways be executed using ng-click and will
overwrite any ng-click value in the display attribute.
The function is passed a deferred object ($q.defer()), if this is wanted to be used `return false;` from the action and
manually call `deferred.resolve();` elsewhere to notify the editor that the action has finished.
restoreSelection is only defined if the rangy library is included and it can be called as `restoreSelection()` to restore the users
selection in the WYSIWYG editor.
display: [string]?
Optional, an HTML element to be displayed as the button. The `scope` of the button is the tool definition object with some additional functions
If set this will cause buttontext and iconclass to be ignored
class: [string]?
Optional, if set will override the taOptions.classes.toolbarButton class.
buttontext: [string]?
if this is defined it will replace the contents of the element contained in the `display` element
iconclass: [string]?
if this is defined an icon (<i>) will be appended to the `display` element with this string as it's class
tooltiptext: [string]?
Optional, a plain text description of the action, used for the title attribute of the action button in the toolbar by default.
activestate: [function(commonElement)]?
this function is called on every caret movement, if it returns true then the class taOptions.classes.toolbarButtonActive
will be applied to the `display` element, else the class will be removed
disabled: [function()]?
if this function returns true then the tool will have the class taOptions.classes.disabled applied to it, else it will be removed
Other functions available on the scope are:
name: [string]
the name of the tool, this is the first parameter passed into taRegisterTool
isDisabled: [function()]
returns true if the tool is disabled, false if it isn't
displayActiveToolClass: [function(boolean)]
returns true if the tool is 'active' in the currently focussed toolbar
onElementSelect: [Object]
This object contains the following key/value pairs and is used to trigger the ta-element-select event
element: [String]
an element name, will only trigger the onElementSelect action if the tagName of the element matches this string
filter: [function(element)]?
an optional filter that returns a boolean, if true it will trigger the onElementSelect.
action: [function(event, element, editorScope)]
the action that should be executed if the onElementSelect function runs
 name and toolDefinition to add into the tools available to be added on the toolbar
function registerTextAngularTool(name, toolDefinition){
	if(!name || name === '' || taTools.hasOwnProperty(name)) throw('textAngular Error: A unique name is required for a Tool Definition');
	if(
		(toolDefinition.display && (toolDefinition.display === '' || !validElementString(toolDefinition.display))) ||
		(!toolDefinition.display && !toolDefinition.buttontext && !toolDefinition.iconclass)
	)
		throw('textAngular Error: Tool Definition for "' + name + '" does not have a valid display/iconclass/buttontext value');
	taTools[name] = toolDefinition;
}