Revert "usermanual: documentation of implemented feature request #9709 (manually adapted from pull request #390)"

This reverts commit eda647408a0e78225b4bf5db67bccb63655da7be.

we temporarily revert these changes as they reflect darktable post-1.4 and we want to
use the reworked usermanual sources for 1.4 already. we can revert this revert later.
usermanual: increase manual version number to 1.4.1