Set the default syntax highlighting to be for plain text files
On branch master, changes to be committed:
	modified:   src/scintillaeditor.cpp
Create the files for a syntax highlighting manager class.
On branch master, changes to be committed:
	modified:   src/Lepton.pro
	new file:   src/syntaxhighlightmanager.cpp
	new file:   src/syntaxhighlightmanager.h
Implement basic functionality (no interface) for the language/lexer manager.
On branch master, changes to be committed:
	modified:   src/syntaxhighlightmanager.cpp
	modified:   src/syntaxhighlightmanager.h