[CAM-13004] Update docs: update outdated Modeler screenshots and remove old sections

The Modeler docs (https://docs.camunda.org/manual/7.14/modeler/) are outdated and require an update.

In particular:

The screenshots are outdated (e.g., old color schema)
The screenshots were manually generated, we should use a script to automatically update them (see https://github.com/camunda/camunda-docs-modeler-screenshots)
Some sections are not relevant anymore
- CMMN is not promoted in Camunda Modeler 4.5+ and can only be actived using a flag. As per PM decision, we shall remove it from this docs page. (Also see https://github.com/camunda/camunda-modeler/blob/develop/CHANGELOG.md for 4.5)
- The "Tips and Tricks" sections gives tips for features that are now considered "standard" (e.g., tabbed modeling). The features can easily be found by the user or are not so important. Therefore we will shall remove this section as well entirely

Maximilian Trumpf added a comment - 20/Jan/21 9:07 AM To be closed with https://github.com/camunda/camunda-docs-manual/pull/828