get_significant_hexes: Get significant hexes
In mrc-ide/PlasmoMAPI: Mapping Plasmodium Spatial Connectivity from Genetic Data

Given a completed PlasmoMAPI analysis, return a list of which hexes are significant outliers.

get_significant_hexes(
  proj,
  empirical_tail = "both",
  FDR = 0.05,
  min_hex_coverage = 10
)

`proj`	object of class `pm_project`.
`empirical_tail`	whether to calculate empirical p-values using a one-sided test (`empirical_tail = "left"` or `empirical_tail = "right"`) or a two-sided test (`empirical_tail = "both"`).
`FDR`	the false discovery rate, i.e. the probability that a hex identified as significant is actually a false positive.
`min_hex_coverage`	minimum coverage (number of edges assigned to a hex) for it to be included in the final result.