Frontools config

[patrykbura]

Problem:
Currently during installation frontools config is overwritten, to work with new child theme.
When there's already a child theme configuration in themes.json it gets removed.

https://github.com/SnowdogApps/create-alpaca-theme/blob/master/templates/frontools/themes.json
https://github.com/SnowdogApps/create-alpaca-theme/blob/master/templates/frontools/browser-sync.json
(themes.json and browser-sync.json)

To do:

• Check if frontools config already exists, edit it in such way that it doesn't brake old theme and adds new changes.