User guide: start pruning tarantool.wiki

Start pruning Tarantool wiki on github, and add documentation
on Tarantool process title to the user guide, since
it is present on the wiki but not in the user guide.

While at it, make the process title more lookalike on Linux
and FreeBSD, and rename some of the (what looks to me as) unclear
process titles.
The documentation reflects the new naming scheme already.