Better verification of header

[DipStax]

Description:

The header of any fix request is verify only by the function fix::Header::Verify, but it doesn't verify the actual value of the different field.

Changed:

Verfiy this field:

• TargetCompId: verify that's the one of the user or the one of the server
• SenderCompId: same as TargetCompId
• BodyLenght: compare it to the actual body lenght received
• CheckSum: verify it's match the calculated one on the request

[gabirel1]

BodyLength / Checksum: #42

[DipStax]

Verification of: TargetCompId, SenderCompId added. Verification of: BodyLenght, CheckSum modify to match the actual verification strategy.