Sort out various brand-specific config files, in custom/brands/<brand name>

project_config.js:
  Brand-specific project packaging configuration, that require cordova
  platform reinit, cannot just be interjected at build time.

custom_config.js
  Brand-specific parameters that are interjected at build time.
Rectify the project_config.json format, and add projectName value.

Node's 'require' needs the values to be wrapped in object notation.
Use projectName from custom/brands/*/project_config.js.

And use absolute paths, determined according to script location, instead
of joins on brittle '.'-prefixed relative paths.