fetching data from sharepoint is very slow

[tripodsan]

Description
the requests to fetch the query index from sharepoint are very slow:

It takes about 4-5 seconds for each request:

• getting the worksheets
• checking for tables
• returning the used range

[tripodsan]

another test, where it's a bit faster (1.5-3 seconds):

[tripodsan]

another one where it takes 2-3 seconds:

[tripodsan]

when supporting #118 it could be reduced it to 1 request, getting the used-range directly, since the table and sheet names are known before.