More User Friendly Interface

[nihadness]

Current behavior before PR

1. In order to go to Sync Views, users have to type exact URL.
2. While Introducing Content Types for any field from Advanced Configuration, users are not able to see the full list of the available Content Types.

Desired behavior after PR is merged

1. Add 'SYNC' to Portal Tab Menu.
2. A very basic page- which users can access directly from 'Add Remote' view, to show all the Content Types existing in the instance.

Screenshots

Link to Sync in Portal Tab:

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Link to show Content Types:

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Content Types Table:

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I confirm I have tested this PR thoroughly and coded it according to PEP8
and Plone's Python styleguide standards.