Revise TableView API for managing the columns

Replace "property list<TableViewColumn> columns" with:
- addColumn(column)
- insertColumn(index, column)
- moveColumn(from, to)
- removeColumn(index)
- getColumn(index)

Exposing list<TableViewColumn> type of property in the public API was
problematic for several reasons. First of all, it limited the internal
implementation too much. Secondly, modifying the list programmatically
did not work as expected, and it also threw nasty warnings while
reordering the columns interactively.

Task-number: QTBUG-30319
Task-number: QTBUG-31028
Change-Id: I0039f7e4be2d6ee9303a4118bdf84146b6a96a05
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Doc: Fix various problems in Qt Quick Layouts documentation

This change fixes the following things in .qdocconf:
 - CamelCase for project name
 - Proper selector for QML Types topic
 - Remove exampledirs since there is currently no example

(Both exampledirs and exampleinstallpath should be used
if examples are added)

Change-Id: I5c56d2e57889fb0e9a94e03222af0cdf2858ddc2
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Change default layout spacing to 5, and make it depend on DPI

Change-Id: I6f34ace6a24ce918cdd417bbfcd2fe8126aa321b
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Move backgroundColor from TableView to TableViewStyle

This property was not respected by some of the native styles
and makes more sense as a styling attribute.

Change-Id: I9cc1d3a130b764a67552ed7f0cec49ccc87ea246
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
MenuItem: Connect to own action's 'shortcutChanged' signal

Otherwise, we won't be setting the shortcut on the platform item.

Task-number: QTBUG-31368
Change-Id: I333b903719d6e95a411f4f423c0e9b8ce15e640e
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Improved size calculation of GroupBox

This adds some pixel tweaks on mac, adds minimum
size to fit the label and fixes dpi scaling on Windows

Change-Id: I4c43ba4a7815be87356336a9dafc1a217437940b
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Rename::tabAt(index) to getTab(index)

The fooAt() type methods are reserved for coordinate based queries.

Change-Id: Iea91bdd29df4fa53cc1c7a07880f466ef2325725
Reviewed-by: Caroline Chao <caroline.chao@digia.com>