modtool: Fixes for intial templates of a block.

1. adds '$' to args in the GRC xml <make> tag.
2. sets <+ITYPE+> and <+OTYPE+> for all I/O data types in io_signature and in work functions to be more clear what needs modification.
analog: (derp) tried to be clever about 2^16 in both Python and C++... failed on both.