When managing data, there will be a preview of test data or validator binary file.
But in PHP7 the prefiew of test data text file or problem.conf text file is not shown.
After my test it is caused by file_get_contents() when passing offset with -1.
It is strange that the manual on php.net in Chinese the default of $offset is -1,
but in English the default of $offset is 0. Use -1 will get nothing, 0 instead is fine.
The commit also change uojFilePreview() that can also be used as viewing binary file.
For backwards compatibility, we just set text as the default file type and no need to specify.
In order to support PHP7, change the way to operate database. PHP7
removed the mysql extension, so the old way to operate database is
not usable. This commit use a new way to operate database.
BREAKING CHANGE: the way to operate database has changed.
