SettingsViewModel implementiert:
update, delete, insert von SchoolYear.

Angefangen:
Änderungen am User
catch error when trying to initialise a persistService a second time
Added check for null of maps
Merge pull request #258 from davherrmann/issue#225

catch error when trying to initialise a persistService a second time
Merge pull request #259 from B3nRa/issue#252

Added check for null of maps
Added form validation for updating/adding teaching materials.
Added first version of manual lending popup and its integration
Some minor UI changes.
Merge pull request #268 from Junkern/issue#205

Added form validation for updating/adding teaching materials.
Merge pull request #270 from henningmu/issue#262-manual_lending

Issue#262 manual lending
Added printing component and integrated it.
Neue Klasse "Properties" zum sessionweiten bereitstellen von Daten
ID in "SchoolYear" eingefügt und SQL-Skripte entsprechend angepasst
SettingsViewModel implementiert.
Funktionen s. issue#239
Merge branch 'upstream/develop' into issue#239-SettingsViewModel

Conflicts:
	src/main/java/de/dhbw/humbuch/model/entity/SchoolYear.java
Deleted unused components replaced by StudentMaterialSelector
Merge pull request #273 from henningmu/issue#266-unify_printing

Added printing component and integrated it.
Merge pull request #274 from davvitt/issue#239-SettingsViewModel

Issue#239 settings view model
Merge pull request #275 from henningmu/issue#204-delete_unused_components

Deleted unused components replaced by StudentMaterialSelector
Fixes detached persistency bug