Backtester updates

Various updates today:

• Added new screens "Bob", "Z26saTA", "Up5X2", "GSX", "Low_Mult" and "WK_Voom". A full description of these and other screens will follow later.
• Adjustment to backtester CAGR and GSD calcuations. The backtester will always attempt to find the dataset closest to the given start and stop dates, taking the trading interval into consideration. The previous version of the backtester used the actual given trading period in the calculations, not the actual average holding period. If you have used "28 days" as a "monthly" holding period, the numbers have not changed, but if you used 30 or 31, the numbers will now be exactly the same as 28 days, since 30 and 31 days will actually fall back to 28 days due to the weekly data resolution. It does not change the numbers significantly, but the new method of calculating it will give a more correct result.
• More runtime error checking. If you have seen jobs getting stuck in the "pending" queue, it is usually because the job causes some kind of runtime error. For some reason unknown to me, at least two people started submitting jobs where the starting and ending dates were mixed up (starting date was after ending date), and this caused a runtime error and the job would get stuck in the pending queue. Fixed now.