Enable folding of code blocks

[tscheburaschka]

Feature request

Like in other language styles, it would be very useful to be able to fold code blocks (if-else, classdef, try-catch, switch etc).

[kornilova203]

We need to implement class MatlabFoldingBuilder extends CustomFoldingBuilder
And register it in plugin.xml like this: <lang.foldingBuilder language="Matlab" implementationClass="..."/>
Example can be found in XmlCodeFoldingBuilder

[kornilova203]

Closed by #63