group vel tomo input file names

[dylanmikesell]

There is a going to be problems with folks trying to use the tomo plugin for high frequency data. For example, when running msnoise p tomo prepare_tomo, the following file is written:
TestGroupVel_0.1sGLISN.dat.

(First, the word GLISN is in there for some reason. I guess this a hold over from Aurelien's original version. I don't see a need for that. The files are likely already in a project folder.)

Second, and more important, the files are named based on period with only one decimal. I am trying to do a tomography from 10 to 30 Hz, with the following periods:
0.033,0.034,0.036,0.037,0.038,0.040,0.042,0.043,0.045,0.048,0.050,0.053,0.056,0.059,0.062,0.067,0.071,0.077,0.083,0.091,0.100,0.111,0.125,0.143,0.167,0.200

When I run the prepare_tomo command, I get three files:

TestGroupVel_0.0sGLISN.dat
TestGroupVel_0.1sGLISN.dat  
TestGroupVel_0.2sGLISN.dat

Each one related to whichever was the last file written in this period band.

0.091
0.167
0.200

Because of the 1 decimal naming convention, the files just get overwritten. It would be very useful to have at least 3 decimals in the file names if we are going to use the period in the file name.