The 'verbose' config file option should be supported uniformly by all commands

[23Skidoo]

Right now, setting verbosity to 2 or 3 in the config file raises the verbosity level for some commands (e.g. install and configure), but not others (e.g. build). This is due to the way the command flags are serialised - installAction and configureAction read in InstallFlags and ConfigureFlags from the config file, but buildAction only parses the command-line arguments (since BuildFlags are not stored in the config file).

The way we handle the --verbosity option seems non-optimal - each *Flags record contains a duplicated *Verbosity field. It looks like it'd be more appropriate to have a single globalVerbosity field in GlobalFlags instead. Then verbosity could be always initialised from savedGlobalFlags.