New feature. Allow user to extend Known Measurements database.

[Roman Telezhynskyi]

In some cases, for example, for coordination several pattern makers in organization would benefit from a feature that allows adding their custom measurement to base of Known Measurements.

This issue related to issue #800.

There is two possible ways to show images. Rely on fact that Tape app knows this measurement and take image from the DB. Or insert image into each record.