[TAP,ADQL] Improve and remake a part of the database connection. Missing javadoc has been added when missing in the modified tables.

TAP: Test better the JDBC connection URL: several syntaxes are possible. Here, the following syntax did not work before this correction: jdbc:postgresql:database (only if it is a local database). Only jdbc:postgresql://host/database and jdbc:postgresql://host:port/database worked!
TODO Parsing of JDBC connection URL should rather be checked again!