[BUGFIX] Saving Page Tree states issues in large environments

Change the way expanded nodes are saved for be_users back to a simple
key/boolean pair and adjust the size of the uc field to fit the needs of
larger page trees.

Change-Id: Ic926080b0dc0e6e24226ab00554091a5f0ffae66
Resolves: #24884
Releases: 4.6
Reviewed-on: http://review.typo3.org/3912
Reviewed-by: Jo Hasenau
Tested-by: Jo Hasenau
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Tested-by: Christian Kuhn
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert