Add commissions for Symbol to cAlgo API

It would be for the cBot to obtain current commission value per million. Now if cBot needs current commission value for a Symbol it either has to look it up from historical trades or open and close a position with a 1K (minimal) amount or have it specified as parameter.
1) Historical trades can have a different commission as happens in Romanov Capital (history of last 30 days specifies the group with different commissions, the more you trade, the less is charged).
2) Opening and closing a position is not elegant and incurs a tiny financial loss.
3) Specifying commissions as a parameter is inconvenient and may be inaccurate due to dynamic commission