Add autocentering of overview

Work funded by Tuscany Region - SITA. Contract "Support to the use
of GFOSS (Geographic Free and Open Source Software) Desktop tools"
(CIG Z3B06FA6D7).
Add unit test for autocentering of overview

Work funded by Tuscany Region - SITA. Contract "Support to the use
of GFOSS (Geographic Free and Open Source Software) Desktop tools"
(CIG Z3B06FA6D7).
Add SIP and Python unit test for overview autocentering.

Work funded by Tuscany Region - SITA. Contract "Support to the use
of GFOSS (Geographic Free and Open Source Software) Desktop tools"
(CIG Z3B06FA6D7).
Fix overview autocentering: always center, not only when the overview is not visible.

Work funded by Tuscany Region - SITA. Contract "Support to the use
of GFOSS (Geographic Free and Open Source Software) Desktop tools"
(CIG Z3B06FA6D7).
Add an update of overview on centering mode switch
pl translation update
[function help] In strpos() needle is string, not number
Merge pull request #872 from Cracert/tr

Polish translation update
Merge pull request #873 from Cracert/i18n

[function help] In strpos() needle is string, not number
osgeo4w: fix shortcut removal
[FEATURE] Paste features as new vector layer
Paste as - new memory layer name dialog
Save as dialog collapsible OGR options
copy/paste as test unit
added change signal to clipboard
set field typeName in gml xsd parser
added date type support
translation update: fi by Kari
german translation update
Merge pull request #665 from Oslandia/overview_centering

[2.1] Overview centering