Fix bug and Implement JDBC read data module, including JDBCDataModel JDBCDataConvertor, etc

[AntiTopQuark]

The main work:

1. Fix the punctuation problem in librec/core/src/main/java/net/librec/data/convertor/TextDataConvertor.java, the default delimiter for csv format files is comma. But it is written as a space in a certain constructor https://github.com/guoguibing/librec/blob/84fc31b4abd5597112cf904235df5d7816438c64/core/src/main/java/net/librec/data/convertor/TextDataConvertor.java#L100-L102

2. Implemented JDBCDataModel and JDBCDataConvertor. And realized a simple test. The database password was processed. The following is a table statement.

   
   CREATE EXTERNAL TABLE `librec_jdbc_test`  (
   `usercol`string ,
   `itemcol` string ,
   `ratingcol` int,
   `datacol` string 
   ) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';

INSERT INTO librec_jdbc_test(usercol, itemcol, ratingcol, datacol) VALUES ('1', '1', 1, '1'); INSERT INTO librec_jdbc_test(usercol, itemcol, ratingcol, datacol) VALUES ('adas', 'cv', 2, '2'); INSERT INTO librec_jdbc_test(usercol, itemcol, ratingcol, datacol) VALUES ('asda', '1', 3, '3'); INSERT INTO librec_jdbc_test(usercol, itemcol, ratingcol, datacol) VALUES ('2', '2', 4, '4'); INSERT INTO librec_jdbc_test(usercol, itemcol, ratingcol, datacol) VALUES ('3', '3', 3, '5');