[FEATURE] Add getters for different media elements

There are 3 new getters to get the specific items directly. This is
especially useful to use e.g. <f:count> on those items.

=> newsItem.mediaTypeImage
=> newsItem.mediaTypeMultimedia
=> newsItem.mediaTypeDam

Change-Id: I2b461de35986eeb520079f197ecb2f7d483bbb95
Reviewed-on: https://review.typo3.org/24141
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
[BUGFIX] Fix error in flexform hook

Resolves: #51961
Change-Id: I098f059ce3eda55db7657c0ce611cb97e7b8c1fa
Reviewed-on: https://review.typo3.org/24237
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
[BUGFIX] Remove exclude from flexforms

Change-Id: If94c6570c21eef028a8661992d3374141e6d7827
Reviewed-on: https://review.typo3.org/24270
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
[TASK] Moved teaser rendering to partials