MySQL Database Model: Execute common MySQL database access queries

This class can execute common MySQL database access queries.

It extends a base model class and executes several types of queries from parameters. Currently it can:

- Query all rows of table
- Query records of a table that match a condition
- Insert or update table records with given field values
- Delete table records that match a condition
- Get single values or single rows from table records
- Check if a table record exists
- Copy records from a table to the same or another table
- Count records of tables
- Generate pagination links
- Manage transactions