Add bash completion for job names

[radomirbosak]

This commit adds suggestion of job names to the bash completion script.
The list of available jobs is stored in a cache file (by default
~/.cache/python-jenkins-cli/job_cache) and is refreshed with every
jenkins jobs call.

Fixes#4

[LD250]

I think we have an issue here.

We have several environments now, so several Jenkins servers. In this case jobs will be cached for all environments. Is it possible to cache jobs on environment level (dedicated cache file for each Jenkins host)?

[radomirbosak]

Good catch! I haven't thought about this.

Note that if always only one environment is used, this is not a problem. With different environments this, however, is not ideal.

I don't see any problems with having cache for multiple environments on the python side (some environment name restrictions/sanitization may be needed). Though it might be a little tricky to get the value of the -e/--environment option in the bash completion script. I'm not that skilled with bash.

[LD250]

I'm not that skilled with bash.

Neither am I

Despite having issue with multiple environments, job completions works well for default one. So I have merged this one.

I have moved this issue to #47