Add Coordinate Reference System to memory provider and delim text provider uri

[ccrook]

This patch adds the ability to specify the coordinate reference system in the datasourceUri for memory and delimited text providers.

The main intention in this is to allow plugins to create these providers with the CRS predefined, so that regardless of the QGIS default providers settings the layer can be created without displaying a reference system dialogue to the user.

Other changes made as part of this: QgsCoordinateReferenceSystem? string constructor has been generalised to allow strings such as "epsg:1234" as alternative to WKT QgsMemoryProvider? datasourceUri can also specify spatial indexing and attributes QgsMemoryProvider? and QgsDelimitedTextProviders? uri's are encoded and decoded using QUrl rather than building as QString, to ensure reliable encoding of special characters QgsDelimitedTextProvider? UI tidied up to correctly remember delimiter settings in QSettings

[ccrook]

Hold fire on this ... Found a few issues so will put up a revised patch shortly :-(

[ccrook]

Should be good to go now...

[ccrook]

And forgot to update the SIP file for QgsCoordinateReferenceSystem?. Now included too...

[ccrook]

Fixed bug in patch - mSkipLines was not being initiallized, resulting in arbitrary behaviour when not defined in URI.

[ccrook]

Found and fixed another bug in delimited text provider. Not related directly to this change, but expedient to include with this. Bug causes to QGIS to crash when reading empty wkt strings. Crash caused in nextFeature where it will attempt to check extents of a null geometry feature.

[gsherman]

Patch applied in r15074 - thanks!