Add helpful messages for longer running functions (cf. devtools::check())

[peterdesmet]

It would be good longer running functions such as:

• read_camtrapdp()
• write_eml()
• write_dwc()

Provided helpful messages (note that the latter two already do to some extent).

Cf. devtools::check() it would be nice if we could change he status from a spinner to a check and indicate the time it took:

✔ reading data (642ms)
✔ creating eventIDs ...
/ updating spatial and temporal scope in metadata ...