Fix drug sensitivity and activity computation

[mauromiguelm]

fixes https://github.com/bigomics/omicsplayground/issues/906

This pull request includes the following changes:

• Fixed drug activity computation for non-human organisms

• Fixed drug sensitivity for CTRPv2 and GDSC datasets for ALL species

• Performed code cleanup and general improvements

Human example

> names(pgx$drugs)
[1] "L1000/activity"     "L1000/gene"

after fix:

> names(pgx$drugs)
[1] "L1000/activity"     "L1000/gene"         "CTRPv2/sensitivity"
[4] "GDSC/sensitivity"

Non human example

before fix

> pgx$drugs
NULL

after fix

> names(pgx$drugs)
[1] "L1000/activity"     "L1000/gene"         "CTRPv2/sensitivity"
[4] "GDSC/sensitivity"