[svn] Added SVN Checkout dialog.
Summary:
Added SVN Checkout dialog with basic and most commonly used SVN Checkout functionality:
- set repo URL;
- change working copy path;
- omit externals.
Additional features:
- automatically pasting repo URL on dialog creation (if its valid);
- automatically forming working copy path based on repo URL (trying to predict repository name);
- user can pick an output folder instead of typing in;
- few error-controls to prevent running 'svn co' with invalid params (disabling 'OK' button).
SVN Checkout can be time consuming.
Reviewers: VDG, Dolphin, meven, elvisangelaccio, ngraham
Reviewed By: Dolphin, meven, elvisangelaccio
Subscribers: anthonyfieroni
Differential Revision: https://phabricator.kde.org/D29489