Sbank change default neighborhood options

Lalapps_sbank contains a set of default options for evaluating a proposal point's "neighborhood" (ie. which points it should calculate matches with). This was well tested using Initial LIGO PSDs (with a lower frequency cutoff of 40Hz). This uses tau0, which is lower-frequency dependent. If one uses an Advanced LIGO noise curve, with a low value of flow (e.g. 10 or 15 Hz) you'll often end up with a double-covered template bank as the neighborhood will be too small.

Here we change the default values to calculate tau0 using 40Hz lower frequency cutoff. This should be good for most use cases for which this would be used in production (and stop the multiple issues we've seen with this in the last year or two). This will probably not be optimal though, so people should investigate setting the relevant values for they're specific use case if they want the code to run quickly .... But it is better that the code take ages, than it give bad output if someone does not think about this.

This is code that I am responsible for, so I'll try to send this to Sarah Caudill to look over and approve. ... I don't seem to have permission to do this :(