Enhance mysql prompt

Update the prompt displayed by the mysql command-line client to include
the username and database in a colour scheme similar to the shell
prompt.
Unify mysql and psql command-line prompts

In order to tell the difference between mysql and psql command-line
clients, each prompt has 'mysql>' and 'psql>' at the end, along with the
coloured username and database information. This makes it easy to tell
which prompt is which when multiple prompts are open.