Introduce and use a Calamares::Branding::setGlobals method.

The method creates a map called "branding" in the global storage, and
inserts an entry for each of the branding strings. This makes the
branding information accessible to the Python modules.

The method is called by CalamaresApplication::initJobQueue.

This is necessary because the Branding class is in libcalamaresui, so
Python modules cannot access it directly.
bootloader: Get the distribution name from the branding.

Remove the redundant "distribution" setting from bootloader.conf.
grubcfg: Get the distribution name from the branding.

Remove the redundant "distributor" setting from grubcfg.conf (and the
entire grubcfg.conf file that has no settings left for now).
bootloader: Ensure that the file names are valid.

Change any '/' slashes to '-' dashes. Also change spaces to underscores
while we are at it.
grubcfg: Quote the GRUB_DISTRIBUTOR value.
branding: Add a shortProductName entry.

This is what the bootloader modules really want, and it was also missing
for consistency with the other branding entries.
bootloader: Use shortProductName.

This is particularly useful if the full product name contains
"GNU/Linux" or "Linux", because e.g. "Generic GNU/Linux GNU/Linux" does
not make sense.
grubcfg: Use shortProductName.

This is particularly useful if the full product name contains
"GNU/Linux" or "Linux", because e.g. "Generic GNU/Linux GNU/Linux" does
not make sense.
hacking/GlobalStorage.md: Document the "branding" dictionary.
bootloader/test.yaml: Define the shortProductName.
Merge pull request #152 from calamares/python-branding

Give Python modules access to the branding information.