Add Lwan tests.

This patch adds Lwan web server alongside a benchmark that implements
all but one (database updates) tests.
Nice to see lots of `&&` in one of these. 

Since you're doing some slightly fancier stuff than the other install scripts, you might want to take a quick skim of how `fw_depends` works [here](https://github.com/TechEmpower/FrameworkBenchmarks/blob/master/toolset/setup/linux/bash_functions.sh#L62)