Ability to mark connection as read only

[rustamwin]

We can add an option like $safeExecution = true and method unsafeExecute().
When condition is empty and safe execution is enabled then an exception should be thrown.

[samdark]

Same feature exists in PhpStorm DB and is very handy. Ability to mark / unmark connection as read only sounds interesting to me.

@Tigrov what do you think?

[Tigrov]

About update/delete without condition. I don't think we should worry about that. This is the developer's responsibility, just like writing an SQL query without conditions.

About read-only option. Looks interesting and could be used for rendering or for Master-Slave connections as a Slave connection.