API: Make leakage, gamma and dir_ex properties

[tritemio]

The usage would be simplified if these 3 correction parameters would be properties.

In this way, an assignemt:

d.leakage = 0.05

would cause recorrecting all the burst data.

Questions:

• How to handle when we do not want to correct (like burst search with nofret=True)?
• Are there any method argumets that cannot be tweaked this way?