New scene selections would have no canvas selected at all.
This would cause issues in places which do not support an empty canvas
selection.
For example, the "scene changed" check of the scene condition would not
work as without any canvas it is not clear which scene to check for.
The "core" macro conditions and actions have been extracted out to the
"base" plugin.
The library now mostly contains functionality which is required across
all plugins and (e.g. definitions for macro segments).
The goal is to reduce the complexity and cross-dependencies and group
the source files in a better way.
This should relsove the "library limit of 65535 objects exceeded" build
issue occuring in some Windows build environments.
