SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
And overhaul resize and paint events to fix layout edge cases in
which Calendar wasn't filling its parent widget completely. Ensures
month views always display prior month days for click navigation.
Converts Calendar app layout to GML.
