Completion is inconsistent #1009

What is the current behavior:

1. If I type select * from use, the first suggestion is user_devices and the 11th is user (with backticks for this one), then other tables like chat_users, and much later come sparse completions like survey_answers.
2. If I type select * from cou, the first suggestion is course, then other tables like course_categories, later enrol_lti_lti2_consumer, then backup_courses.
3. If I type select * from _cons, there is no exact match in the near 20 suggestions. I need to add an extra letter (_consu) to find the exact match enrol_lti_lti2_consumer.

What I expected:

• The table names starting like what I typed should always come first, in alphabetic order. In case 1, user should have been the first result, just like course was the first result to 2. Backticks should not interfere in the sorting.
• Exact matches should always come next. In case 2, backup_courses should precede enrol_lti_lti2_consumer (where cou is not present). In 3, the exact matches could only be found through scrolling, which is not the expected behavior.

Other grieves (I won't create an issue for each one, feel free to do so):

• There should be a configuration switch to disable sparse matches. IMO they just adds noise to the suggestion list, as case 3 clearly shows.
• The completion should be sensitive to upper case input, so that Cou should match Course but not discourse.
• Pressing Escape while in the suggestion list should cancel it.
• Pressing ctrl-g does cancel the suggestion list, but it should restore the user input.