remove snapshot-website-base in snapshot engine; download it instead

[nicolasochem]

the _config.yml in xtz-shots-website and snapshot-website-base is identical except for one line.

Instead, let's have these 3 config in values.yaml:

jekyllRemoteThemeRepository: oxheadalpha/xtz-shots-website
jekyllConfig: https://raw.githubusercontent.com/oxheadalpha/xtz-shots-website/master/_config.yml
snapshotMarkdownTemplate: https://raw.githubusercontent.com/oxheadalpha/xtz-shots-website/master/snapshot.md

Then the website builder job:

• downloads jekyllConfig
• adds remote_theme: oxheadalpha/xtz-shots-website to the downloaded config based on the jekyllRemoteThemeRepository param
• uses this config to build the remote theme

[harryttd]

related to #418