Add option to delete a stage, corrected syntax of node-sass

[rupav]

PR solves the issue #26 and #34 .
**#30 was the PR mistakenly merged into the codebase, which disrupted the commit history locally for me. Now this PR solves the problem of #41 **

Explanation About What Code Achieves:

• Explanation
  in PipelineEditor I made a button element, attached it to all stages of the pipeline, then with onClick event handler, I dispatched an action to remove node/stage, (with node.code and active document helping me to find out which stage needs to be removed). Reducer copies the previous state, then remove the desired one, and returns the updated state.

Screenshots/GIFs:

• GIF for the changes:
  

Steps To Test:

• Steps
  Clone the changes, then run python -m candis from the root of the directory.

TODOs:

• Delete the stage, write it to the file.
• Also after removing any 1 stage, adding another stage causes error as can be seen in the GIF, note ( as per error my directory dont exist, but it actually exists ).
• Styling of the button needs to be done.

Now one can delete a stage from the pipeline successfully, get it saved to read the pipeline next time with modified content.