Doc: Move and edit examples page

Changed the example page type to a group to have a standardized
table of examples. Also, a filename 'examples.html' is too
collision-prone when Qt docs are output to a single directory.

Also, moved the examples.qdoc file into /doc subdirectory to
avoid it from being copied to QT_INSTALL_EXAMPLES when packaging
the examples.

Change-Id: I87251e0fde127bdef3024907b6472b50039f0357
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Doc: Add generic thumbnails for the examples

As the examples do not have any images in their documentation,
no thumbnails are generated.

This change adds generic 'Qt Code Sample' thumbnails for the
examples, ensuring that they are listed in Qt Creator's
example list.

Change-Id: I40d3c69e9cebad72997d82eba0758c63c146aea7
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Doc: Language/writ. guidelines review Qt WebSockets

Task-number: QTBUG-37149
Change-Id: Ic0c28928404fc515de40e6fdff11849cdb2929d6
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
fix typo in macro

Change-Id: Ib302db81e0667d0c89c1da8611639db0811ff9f3
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
fix compilation with QT_NO_NETWORKPROXY

Change-Id: Ice7ad51cbbde0ef2459642309c32dd392463754d
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Doc: small fix in documentation

Change-Id: If7c0e3f33c8c73695492511ff51ab58f4a7863d0
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Move examples into 'websockets' folder

In the packaging process the content of all 'examples' folders are
copied together into one folder ... so modules are supposed to have
their submodule name as a sub-folder of 'examples'.

Change-Id: I9981b914e8268c932ca5a3d1c9fa73f8db0b6a5b
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Doc: Fix example path in documentation config

Task-number: QTBUG-37643
Change-Id: Ifce8f4016c70642a7ae344b0bab463eb201460df
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Change-Id: I7215c289188462383799269aa9b736ae76db4d25