[ajax] Rename "request" to "fetch"

[ruphin]

We propose changing the ajax.request() and ajax.requestJson() API to ajax.fetch() and ajax.fetchJson(), to align more closely to platform naming conventions. This change will:

• Help users understand more intuitively that these have the same function signature as the Fetch API.
• Avoid confusion with Request when discussing this API.

[ruphin]

I have prepared a branch with the suggested change here: https://github.com/ing-bank/lion/tree/chore/ajax_rename

[daKmoR]

change looks good - feel free to open a Pull Request once you think it's ready to be merged

[jorenbroekema]

#1371 taken care of here :) thanks!