2) Use 'format' instead of f-string for compatibility with Python 2

2) Fixed import statements - don't use `from x import *`, but import only what is needed.
2) Reformatted the code.

try to fix version check chokes problem according to grafana's current version format. https://github.com/ysde/grafana-backup-tool/issues/37

The current solution does not allow the GRAFANA_HEADERS to be optional. Pulling the if statement outside the dictionary comprehension to allow the variable to be optional.

The search_api_limit must not be larger than 5000 since April this year (grafana/grafana#16458). I figured this out today after upgrading grafana to 6.4.4 from 5.something.

Probably we should fix the search_dashboard() at some point to use pagination (for sites with more than 5000 dashboards, folders, datasource).

Continue working on PR#25 (https://github.com/ysde/grafana-backup-tool/pull/25):
* move all python into src/
* delete boilerplate restore_SOMETHING.sh scripts
* update README.md
* add some things to .gitignore