Add MonetDB server environment variables to MonetDBLite

We could add some of the MonetDB server environment variables during MonetDBLite database startup. This could be useful in some environments.

Start database on read only. (readonly)
The total number of threads to be used during query execution. (nthreads)
Maximum number of clients in order to limit thread creation. (nclients)
MAL optimization pipeline, but this can be changed with a SQL statement. (optpipe)

hannes / MonetDBLite