Shell import export

* no welcome message with command mode (-c), also configurable with -Dquiet=true
* shell variables passed to cypher queries as parameters
* last cypher result row content set as shell variables
* allow json for shell variable values, maps, arrays, etc
* dump command for exporting a db or the subgraph of a cypher statement
* can reassign shell variables, export a=10 && export b=a -> b=10
* shell can execute a contents file directly with -f file which is faster than piping via stdout