* Allow to specify a custom username in "pmbootstrap init"
* Build chroots have "pmos" instead of "user" as username now
* Installation user UID is 1000 now (as in all other Linux distributions)
* Adjust autologins
* postmarketos-base: enable wheel group for sudo, removed previous sudoers file
* Implement safe upgrade path:
We save the version of the work folder format now, in $WORK/version.
When this file does not exist, it defaults to 0.
In case it does not match the currently required version
(pmb.config.work_version), then ask the user if it should
automatically be upgraded.
* The system image size is now calculated as: root size - home size.
* New function in `pmb/helpers/other.py`: `folder_size()`, with a
testcase.
* Instead of copying everything to the system image folder, and
deleting the home folder afterwards, do not copy the home folder
in the first place.
* Added `pmbootstrap -s` to skip generating the initramfs for faster
debugging.
* Set the default value in the "are you sure, that your partition has
at least..." to "y", so we can run `yes '' | pmbootstrap install`
to make it run through the whole installation process.
* Increase full size to 120%, boot partition gets 15 MB free space now
* Update runtime error message thrown for grsec/hardened kernels, saying that they are not supported right now, #107
* Remove unnecessary check for grsec enable/disable status - the build will not work in either case
