Add default arguments to diff tool

Add two essential default arguments to the diff tool class.
Also add a hard-coded list of default recognised arguments to the
diff tool info edit form.
Add minor changes to name checks

Diff Tool name check minor changes - minimum number of characters is
returned to being a constant value.
Merge branch 'settings' into hydrogen

Conflicts:
	FunctionMerge/DiffToolInfo.cs
	FunctionMerge/DiffToolInfoForm.cs