`PlotSignatureTransformed()` function added

[LotharukpongJS]

Implemented PlotSignatureTransformed() and some minor changes:

• PlotSignatureTransformed(), which complements PlotSignature() and tfStability(), has now been implemented.
• gridExtra::grid.arrange() is replaced with ggpubr::ggarrange().
• PlotSignature() now also works with the TestStatistic = "LateConservationTest", first implemented in #11 . This lack of functionality had been previously overlooked.
• Rebuilt the package website with pkgdown::build_site().
• Fixed the issues with devtools::check() after #17
• Addressed #16 (adding p-values as subtitles).
• Updated some of the documentation, including the pseudocount parameter description for

For PlotSignatureTransformed():

PlotSignatureTransformed(ExpressionSet = PhyloExpressionSetExample,
                         TestStatistic = "ReductiveHourglassTest",
                         transforms = c("log2", "sqrt", "none", “vst”, “log”, “rank”, “squared"),
                         modules = list(early = 1:2, mid = 3:5, late = 6:7))

[LotharukpongJS]

Removed non-standard files/directories.

[HajkD]

Wow!!! Brilliant work, @LotharukpongJS!

Looks perfect to me!