In Open From Library dialog, open R script file and write to the Script Window, also added Niger script file

[N-thony]

Fixes #6984
This PR adds the Niger script file to the Climatic > Niger folder and also the facility to open an R script to the Script Window from Open From Library.
@africanmathsinitiative/developers @rdstern this is ready for review. Thanks.

[N-thony]

@lloyddewit I have resolved your comments above. Please take a look. Thanks

[lloyddewit]

Thanks, just a couple of small suggestions for readability

[N-thony]

@lloyddewit I resolved your comment above. Please take a look. Thanks.

[rdstern]

I first tried with the script window empty and it worked fine. It also didn't ask me - which it used to - and was unnecessary.
So - good so far.
Then I tried with a second file and with something already in the script window. It warned me - that's good too.
So I said no (I realise I should have tested yes as well, but didn't.) Anyway after no it returned me to the ordinary Import file dialogue with that R file. So I pressed Ok and it gave me an error.

Two points follow from this:
a) It would be good if the Import dialogue could also recognise an R-file and put it into the script window. Currently the only way is via right-click once in the script window.
b) A separate point is whether it should go to the import dialogue when I say No to overwriting the existing file in the script window. I'm not sure about this.

[N-thony]

I first tried with the script window empty and it worked fine. It also didn't ask me - which it used to - and was unnecessary. So - good so far. Then I tried with a second file and with something already in the script window. It warned me - that's good too. So I said no (I realise I should have tested yes as well, but didn't.) Anyway after no it returned me to the ordinary Import file dialogue with that R file. So I pressed Ok and it gave me an error.

Two points follow from this: a) It would be good if the Import dialogue could also recognise an R-file and put it into the script window. Currently the only way is via right-click once in the script window. b) A separate point is whether it should go to the import dialogue when I say No to overwriting the existing file in the script window. I'm not sure about this.

@rdstern I resolved your comments above, please take a look. Thanks,

[rdstern]

@N-thony this now works perfectly - though with a big "but"!
As far as I have tested the File > Open From Library seems to work ok. (As I write this I realis that I haven't tested fully when you load a sequence of R files and then a data file and then an R file again. So that will be good to check.
But, now the new code interacts with the File > Input from file dialogue, and in a pretty fundamental way.
a) I had a file in the script window. When I use File > Import File (instead of Input from library), it gives me the warning that I would expect from the Input from Library dialogue.
b) So I cleared the script window and tried File > Import again. Then it returned the previous script automatically!
Now I would also like the File > Import File dialogue to be able to import a file into the script window. I assumed this would be a separate issue, but perhaps it may be simpler to add this feature to the File > Import dialogue now???

[N-thony]

@rdstern the change I made temporarily resolved your comments above. With a possibility to import an r script From both File and Library.

[rdstern]

@N-thony great - this seems to work now.