Improve quality of the Text scans.

Text scan (Gray) have less information to process, that't why is about 3 times
faster than color mode. Unfortunately the quality of text scans are not good,
as it is converted to 2 bit (black and white) images.
To improve that conversion to black and white images was disabled.

As a result the images have good quality, and the scanning process is fast.

To scan images to black and white, the Lineart mode should be used.
Unfortunately it is not supported by UX design.
3 jobs for use-better-quality-for-text in 2 minutes and 38 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #673114
build-arch

00:01:50

passed #673113
build-fedora

00:02:31

passed #673112
build-ubuntu

00:02:38