Implementing TRestAxionXrayWindow using TRestPatternMask

[jgalan]

This PR takes into account the recent TRestPatternMask implementation to redefine the implementation of TRestAxionXrayWindow.

• The data directory structure has been updated and pipeline as well in consequence.

• Replaced TRestAxionXrayWIndows metadata members by TRestPatternMask.

• Documentation updated accordingly.

[ruzarmen]

Nice!
I like it! Not sure why we constrain to 8mm radius, there must be a reason for it though.
I am approving the PR

[jgalan]

For the moment all definitions are dummy. Once we can build the full setup, we will be able to define any window size through a different RML definition. We will then perform the MonteCarlo with different window sizes, if desired. And with the official window size from Micromegas and InGrid.

[jovoy]

Ah yes, the 8mm were just a prototype we were thinking about that is even thinner than the 14mm windows so that's why it's an example here but as Javier said you can put other window parameters in. If you upload the Micromegas window parameters to confluence (or ask someone else to do it) we could also already put it in a RML file.