Add possibility to pass additional command line arguments to the "PostgresProcess.export*" methods

[oilid]

There is currently no possibility to specify additional arguments to the pg_dump command (for example to specify the export format by "--format=format"). This issue belongs to all PostgresProcess.export methods. An example how this could be implemented is already realized in the import method "importFromFileWithArgs" or "restoreFromFile". This change request concerns to the following methods:

• PostgresProcess.exportToFile
• PostgresProcess.exportSchemeToFile
• PostgresProcess.exportDataToFile

I just realized this issue in my fork (backport java 1.6): https://github.com/oilid/postgresql-embedded/commit/f6583e82bdf3f6f6d78d9fb65b65116545c5e846