Add get timestamp from snapshot function

[Raufabdul8]

This pull request resolves issue #3 by making a common function for getting timestamp from snapshot filename.

[timea-solid]

Hi @Raufabdul8. Thank you for your PR, it is a really needed cleaning of the code!
However it does not solve issue3. I think my description of the problem was not clear.
Now the '.ttl' file type is hardcoded -> this is the problem. It should read the file type from the name of the file and reuse it.
What you refactored is a much appreciated preliminary step.

[Raufabdul8]

Added a simple fix to handle most file extensions.

[timea-solid]

@Raufabdul8 brilliant!
Now last step (we are very close) ->

SolidHelloWorlds/src/adminPage/snapshots/snapshot.js

Line 40 in 3b2c8b4

let docName = nameOfSnapshot + "-" + timestamp + ".ttl"

nameOfSnapshot now comes from a config but it should be the same name and file type like the one we make a snapshot of.