[CMAKE] Rename the top-level and src/ cmake projects
The same project name (BitcoinABC) is actually used at both level.
This would cause the src/ project properties to override the top-level
The new names are chosen to be consistent with the other cmake project
cmake -GNinja .. ninja
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D4027