Single "Row Count" keyword with Assertion Engine

[amochin]

There are currently 5 "Row Count" keywords - one just returning the row count and four with assertion (equal, great/less than).
This can be replaced with a single "Row Count" keyword only - if we integrate the Assertion Engine like in the BrowserLibrary

Maybe even replace the "Check if (not) exists in DB" keywords?

[amochin]

There are 2 new keywords using the Assertion Engine:

• Check Row Count
• Check Query Result

The Row Count keyword is left untouched - just for returning the row count, without any checks.
The following keywords are marked as deprecated now and will be removed in future versions:

• Row Count Is 0
• Row Count Is Equal To X
• Row Count Is Greater Than X
• Row Count Is Less Than X
• Check If Exists In Database
• Check If Not Exists In Database