Added contextMenu component

— The context menu is opened with the open() function. This function
can be called from a HTML element’s on-contextmenu (i.e. <element
on-contextmenu=“contextmenu.open()” />).
— Menu options for the context menu are defined as an array of objects.
Each object can contain the following
  — content: The text to display in the menu and to save as a selected
value
  — class: CSS class for the <li> element in the context menu dropdown
(can be used to insert dividers, for example)
  — value: Value to be saved when selected, overwrites content as value
if provided
  — action: Function to be run when the option is selected
— Actions to be taken when selecting a menu option can be
— A delayable event “open” is triggered before opening the context menu
— The “select” event is triggered after a option has been selected and
the option’s action function (if any) has been called
Merged branch contextMenu into master