KCM/Autostart Add a model to separate logic from UI

Summary:
Adds the complete fileName of the autostart entries as tooltips.
Collapse home to ~ in command column.

Test Plan:
 * Add a desktop entry
 * Edit a desktop entry
 * Disable a desktop entry
 * Remove a desktop entry
 * Make a destktop entry run only in KDE
 * Add a script Item with symlink
 * Add a script Item without symlink
 * Change the startup choice for a script Item
   * Add twice the same script to the same startup choice
 * Remove a script item

Before:
{F8133419}
After:
{F8133420}

Reviewers: mlaurent, ervin, #plasma, broulik, bport, crossi

Reviewed By: ervin

Subscribers: alex, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26934