PEP8 fixes for the blagui package

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
blaview.py: remove some excessive code duplication

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
Replace membership tests through lists by tuples

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
Unify the border width and padding of widgets

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>