Fix warnings introduced in Xcode 9

Fix vertical alignment of 'Paste' button in advanced paste.

actually allows this if screens don't have their own spaces. Issue 6125

This fixes both deadkeys alone (e.g., ` on a DE keyboard) or deadkey+key (opt+` on DE to give '). I tested migration from 3.0 and it seems fine.

If no local authentication policy can succeed, then authenticate the password manager. This is the previous behavior from 3.1.1. Apparently OS X 10.11 has the APIs but can't authenticate with them. Issue 6113

Disable High Sierra's system tabs, which you can get when System Prefs > Docks > Prefer tabs when opening documents is set to Always. Issue 6096

Add +[NSObject castFrom:]

Fix a minor typo

Fix a bug where thin strokes be used when the setting was "dark background" or "retina + dark background" even when the background was light because the background color didn't get passed through since we dididn't want to split up ligatures on background color changes. Since the thin strokes setting means the foreground depends on the background, the background color must be passed through and ligatures will be broken if the background color changes within them. Issue 6027

This is a minor typo in the advanced prefs UI

Make background single-use commands use system() instead of opening a short lived window because it goes nuts when this is done in a fullscreen desktop. Issue 6033

Fix bug where tags weren't visible in toolbelt profiles list because the cells weren't tall enough because nstableview is a big old mess. Issue 6056