Cosmetic changes for search entry and delete dialog

Search entry "Cancel" button now uses symbolic icon, turns to "error" color (red) when active. Search symbolic icon turns insensitive when text not entered.

Fixed a bug where the "Begin Search" tooltip wasn't showing when hovering the search icon.

Search Entry now expands in CSD mode, more similar to how it looks in Classic mode.

Adds "destructive-action" class to Delete button. Most themes will color this a "danger" or "destructive" color, red in most themes.

Use symbolic icons for delete dialog buttons. Went with window-close-symbolic for Cancel as there is no symbolic icon for cancel. Usually it's an X similar to cancel, but some themes might use a different icon (like shutdown). If you want me to change this I can. Might be better to just use text-only buttons here.

Increased default window width slightly since sidebar is on by default now. Increased default window height to account for extra "Modified" filters previously added.

Switched deprecated margin-left and margin-right properties to margin-start and margin-end.