Sequence diagram Loops: changing boxMargin spoils the "loop" notation

[LarryKlugerDS]

In Sequence diagrams, a loop section draws a box with the word "loop" in the top left corner. This is all good. In addition, the title of the loop is in the center of the box, near the top of the box.

To add a bit of margin between the Loop title and the line at the top of the box, change the configuration field boxMargin

Problem: by error, the boxMargin is also used for positioning the "loop" label. SInce the loop label is in a fixed small place, changing boxMargin causes the word "loop" to move out of its box.

Fix is in the pull request.

[tylerlong]

PR had been merged long ago: #300

Closing.