This adds a tooltip to all the slider properties showing their
current value. Previously there was no indication of what
value they had. Also rename the SprayTool property 'thickness' to
'size' like BrushTool calls it.
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 *
