update default partitions size

Given Tails + Wheezy’s ISO size and the actual, real-world incremental update process space requirements (#5764 (closed)), the good old space requirements (2GB medium) and system partition size (1.5GB) may need an update.

Feature Branch: feature/bigger-system-partition

Parent Task: #5490 (closed)

Related issues

Related to #6015 (closed)

Original created by @tails on 5834 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information