license: License changes on various portions of the codebase

Where possible (and with contributor permission), items have been
changed to LGPLv2.1 or MIT licenses to avoid issues with any proprietary
libraries from vendors (HDL and FW), allow static linking (with headless
mode operation in mind), and to generally present users with more
permissive licenses.

File headers and the COPYING have been updated accordingly. Third party
sources have been either removed, replaced, or relocated in the source
tree, in accordance with the licenses decided upon for each part of the tree.

Contributor Assignment Agreements have been added, and it is required
that these be submitted before significant patches and pull requests
are accepted.
Update debian/copyright to match current state

Second/third/fourth pairs of eyes are welcome...

h/t to A. Maitland Bottoms' Debian package for spotting the
Altera and OpenCores packages