Improvements and fixes

A ticket can now be set to "Private" and is then seen only by the people it involves.

• Anyone who can read a plant's tickets can comment on one set to "Private".
• An email about a support reply is no longer sent while the thread is open.
• The ticket and support lists now show the latest comment or message under each title, and a dot marks what is new.
• Numbers in notifications about plants, such as an irradiation value, now read as whole numbers.
• A grid-operator shutdown or an external curtailment command now opens as a normal-priority event instead of a high-priority one.