Implement custom token based parser instead of RegEx filtering

[Tim-Maes]

Currently T4Editor is leaning heavily on the use of RegEx patterns to filter out codeblocks from the textView and colorize them.

A better approach would be to create something that parses the textView on a token based implemenation. We only catch the T4 open/close tags and this leaves room to try and introduce C# language features inside these blocks.