Add files via upload

[Periscope-NZ]

Add .xlsm (Microsoft Excel macro-enabled spreadsheet) to the type lookup. XLSM files are supported by Power BI but until now they could not be uploaded, refer to issue microsoft#349

Fixes microsoft#349.

Changes proposed in this pull request:

• Adds a single line to Get-ItemType.ps1 for the .xlsm file type
• Minor reformat of layout (spacing) for neatness

How to test this code:

• Create an .xlsm file in Excel
• Upload the file using `Write-RsRestCatalogItem -ReportPortalURI $youruri -Path 'C:\Temp\Just_a_test2.xlsm' -RsFolder $DestFolder'
  Previously this would fail with an error message - (400) Bad Request. After this change to Get-ItemType.ps1 it seems to run without any issues.

Has been tested on (remove any that don't apply):

• Powershell 5.1
• Windows Server 2016