Use symbol table to generate fresh names in InsertRefCounting

[j-hui]

• Add name mangling pass to make VarIds globally unique
• Use slightly more esoteric mangling to avoid clashes
• Actually update the varNames map
• Make LambdaLift use manglenames
• Fix Lambda lift pass
• Fix things after different binder structure
• Still broken, waiting for types to appear in binders
• Ok ok ok ok
• Get it compiling
• Passtests
• Some small fixes
• Use symbol table to generate fresh names in InsertRefCounting

[j-hui]

actually, no point in breaking up this into a separate commit. This commit will be rolled in together with #120