[QGIS-Developer] Processing Gdal Help issues

[matteo]

Hi,

while QGIS algorithm, despite all the anchors issues we are solving,
some GDAL button links to the GDAL page and not to the QGIS page. I
found these:

* Clip raster by extent
* both algorithm in "Vector conversion"
* all algorithms in "Vector geoprocessing"
* Import vector in PostGIS database

I think all of them should point to QGIS webpage and there we can add
links for gdal official documentation

Cheers

Matteo