[FEATURE] ext:install Core update

The patch provides the code infrastructure to test for possible
core updates using information from get.typo3.org and implements
a "one-click" update within "important actions".

The update itself is implemented as a list of ajax calls performed
after each other to have minimal impact and side effects to current
core code.

The service classes "CoreVersionService" and "CoreUpdateService"
contain the main business logic and may be used in a reports module
or scheduler task later on.

Change-Id: I5947252ca805b237b513fdafcf2696e9da586fc0
Resolves: #52547
Releases: 6.2
Reviewed-on: https://review.typo3.org/24396
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel