Mathview Upgrades

I've made some upgrades to mathview
1) Mathview shouldn't look janky on smalls screens (test by making a thin window).  Its not particularly easy to use but thats a problem for another day. 
2) It now supports latex editing.  Just add the class latexentryfield to a text area and it will make a button for a mathview latex edior
3) Added this mathview latex editor functionality to PGProblemEditor2/3.  It can be turned on and off by setting $options{PGMathView}=1 in a configuration file.  

Someone should test that MathView still works as expected on homework problems, and they should enable the config variable and test that it does latex editing correctly for PGProblemEditor2/3.