Add warning for cf_cosine_plot when initial ids dropped

[mmc46]

When the ids provided to cf_cosine_plot don't have enough connectivity they're silently dropped. The function output notes how many connecting partners are dropped.
It would be useful if there was a warning listing which initial ids were dropped, if any.

library(coconatfly)

test_hc=cf_cosine_plot(cf_ids("type:DNpe008", datasets = c("flywire", "malecns")), heatmap = F)
Updating 6669 ids
Updating 5487 ids
Matching types across datasets. Dropping 489/533 output partner types with total weight 9305/9704
Matching types across datasets. Dropping 274/503 input partner types with total weight 3155/5972
Warning message:
In Matrix::cov2cor(cpx) :
  diag(V) has non-positive or non-finite entries; finite result is doubtful

test_meta = cf_meta(test_hc)

length(mcns_ids("type:DNpe008"))
[1] 18
length(flywire_ids("type:DNpe008"))
[1] 18

test_meta %>% count(dataset)
  dataset  n
1 flywire 17
2 malecns 18

[jefferis]

Closed by #26