[FEATURE] Custom active tab in RTE element browser

Introduce a flag that prevents the element browser of rtehtmlarea
from overwriting the active tab that was set by a hook object.

Resolves: #49036
Releases: 6.2
Change-Id: Iebfda39714caa98c0d2023992bbf63a2f5b9b01a
[FEATURE] Allow custom record list in element browser

Introduces a class variable and a setter for a custom record list
instance in the element browser that can be used to override the
default element browser recordlist.

Resolves: #49037
Releases: 6.2
Change-Id: I41fd3a33f70e72aedef9362ee6bf67de9dcde8ac
Merge branch 'issue_49036' into TYPO3_6-2-allfixes
Merge branch 'issue_49037' into TYPO3_6-2-allfixes