Better error message for failed setTypeCreator

[adomasven]

Lots of reports with

[Exception... "The file �Zotero.dot� couldn't be opened because there is no such file. @[setTemplateTypeCreator:install.m:223]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: file:///Applications/Zotero.app/Contents/Resources/extensions/zoteroMacWordIntegration@zotero.org/components/zoteroMacWordIntegration.js :: checkStatus :: line 213" data: no]

We should return something much more descriptive, like

Zotero failed to install the plugin files into /Applications/Microsoft Office 2011/Office/Startup/Word. Please ensure that Zotero has write permissions and the directory exists.

[dstillman]

People are still encountering this error and getting confused:

https://forums.zotero.org/discussion/84461/installing-word-add-in-from-command-line-or-with-filewave (and many others)