Make windows use native window decorations by default

[zjeffer]

Users have reported (#521) that it would be better if Windows used native window decorations by default. This PR sets that.

(not tested yet but I assume this small change works fine)

Closes #525

[guihkx]

In my opinion, we should not be changing options set by the user (as some may prefer custom decorations, for example).

A safer approach, in my opinion, would be using native window decorations by default when our config file is not present (i.e., it's the first time the program is running).

[zjeffer]

A safer approach, in my opinion, would be using native window decorations by default when our config file is not present

That's what this PR does, no?

[guihkx]

Oh, you're right. The second parameter of value() sets the default one.

In any case, I'll test this shortly.

[guihkx]

Works on Windows 7!

A minor styling choice nitpick: I'd use #if defined(Q_OS_WIN) instead of #ifdef _WIN32.

Other than that, LGTM.

[zjeffer]

Thanks for testing!

[zjeffer]

@nuttyartist On the get-notes.com homepage, under the "Cross-platform" header there's a screenshot for every platform. I think we should update the Windows screenshot with one using native decorations now.