Optimize layer transformation in App

[HDouss]

The analysis process (analyze method in App class) is building a chain of xsl layer files. The skeleton transformation by these layers is done for every xsl report, to be given as input for that report.:

new XslReport(
    chain.transform(skeleton), xsl,
    new ReportData("...", this.params)
)

chain.transform is called as many times as we have reports.
We could do this transformation once and for all and give the result as input to the reports.

This will make this process faster by doing this only once.

[0crat]

@paulodamaso/z please, pay attention to this issue

[HDouss]

@paulodamaso ping

[HDouss]

@paulodamaso ping

[paulodamaso]

@HDouss I think that it will be easier to do this after #461

[HDouss]

@paulodamaso I don't really think it is related, here it is only about chain.transform(skeleton) that is repeated for every XslReport. But anyway, do you agree it has to be done?