rose.config: ban square braces in section names

Section names are no longer allowed to use the open and close square
brace characters.
rose.config: improve pylint and pep8 scores
Merge pull request #1359 from matthewrmshin/config-disallow-square-braces-section

rose.config: ban square braces in section names
File install: consider access mode as well

Access mode is now stored, and compared in incremental install.
Use file timestamp+size instead md5sum for rsync install.