cmake: Added custom NSIS templates

* Unused "gnuradio Desktop icon" option removed
* GNU Radio Companion can now be accessed from the Start Menu
docs: Manual pages for OFDM and packet tx/rx
runtime: changed block_gateway's include of feval.i to import
Merge remote-tracking branch 'martin/next-docs' into next
Merge remote-tracking branch 'ncorgan/nsis_improvements'
Merge branch 'master' into next
blocks: add set_msg callback and api update to grc block_message_probe