New Feature: Search Functionality

I have added Search functionality to Snap!, which allows users to Search for blocks by name. It finds standard, Global custom, and Local custom blocks, as well as variables, the Make a block and Make a variable buttons. It works in all languages supported by Snap! There are two small issues that I have not been able to figure out though: The text on the "Search" button is not initially centered correctly when it is created, and ToggleMorphs do not update their look when they are pressed in the Search category (They do complete the correct task though)