Submodule merge

Ok, this one is a biggie. Note that the 595 commits are mostly from https://gitlab.esss.lu.se/epics-modules/require, so can be "ignored". Commit ba540f05 is the first relevant commit related to the restructuring, the rest are so that we keep the history of require and include it in the history of e3-require (see https://medium.com/walkme-engineering/how-to-merge-a-git-submodule-into-its-main-repository-d83a215a319c).

I have done the following tests:

• Built and made new require, run iocsh.bash. All is well
• Rebuilt everything with this module, hashes 363753f68 and 873d9e84d using the compare tool from https://gitlab.esss.lu.se/e3/e3 - the only differences are those that are expected.