Add USING PERIODIC COMMIT to Prettifier

o Untangle Prettifier parser along the way
Add support for FIELDTERMINATOR in LOAD CSV and remove ROWTERMINATOR from the parser
Convert PrettifierTest to CypherFunSuite
Merge pull request #2069 from davidegrohmann/2.1-loadcsv-separators

Add support for FIELDTERMINATOR in LOAD CSV
Fix LoadCSVPipe ask for a CSVIterator with the specified custom field terminator
Add reference documentation for Load CSV
Merge pull request #2070 from boggle/2.1-pc-prettifier

2.1 Prettifier support for USING PERIODIC COMMIT
Merge pull request #2071 from davidegrohmann/2.1-loadcsv-docs-and-field-terminator-fix

Load CSV reference docs
Fix handling of null property values for nodes in CREATE, MERGE, and SET

o Create ignores
o Merge throws
o Set removes