Fix of delimited text provider to handle CSV files including quoted newlines properly 

This change makes a number of updates to the Delimited text provider, of which the main one is that it can now read CSV files with newlines within quoted fields, and escaped newlines.  Also adds option of choosing geometry type for WKT data in CSV files (point/line/polygon) which filters out other geometry types, file encoding, files without field names in the first record.  UI changes to access these options.

Also added test cases for the delimited text plugin.

Also updated qgsvectorlayer.h with documentation for the main vector providers, to the best of my knowledge (limited for some of them).  Thanks to Jeremy Palmer for the text on the WFS provider