Meshmoon core fixes pt. 10

Some minor tweaks, a crash fix, issue/bug fixes and live monitoring of attribute metadata changes in ec editor.

Could not include all changes as same commits had Meshmoon related parts or the file conflicted too badly vs core. Someone might want to copy the relevant code parts from these commits directly to core:

* https://github.com/Adminotech/tundra/commit/d7d7c3ab2748ee5ab3b9e6a52168e24d36da54b2#L0R21 (no need to pull this, it was reverted in the last commit in this list)
* https://github.com/Adminotech/tundra/commit/873c953e22626421b2884b06f45cd7311d7d073d#L0R266 (leave out the license copying, its meshmoon specific for now at least).
* https://github.com/Adminotech/tundra/commit/f33c6e3b445adf57a22646a30da8f52b5d681859#L0R5 (updating min cmake version and the `cmake_policy(SET CMP0005 NEW)` part and changing to direct add_definitions without cmake variables.)