Improve Theme cover based

[cuong-tran]

• Support Pure dark mode
• Tag using elevated style (non pure-dark-mode) and more vibrant outline color (pure-dark-mode)
• More color for various icons
• Color theme for Metadata screen
• Always animated color change
• Always/Only use dominant color for library/update/upcoming cover's background
• Don't always generate color each time cover loaded (library/browse), only update color when new cover changed on detail page
• Fix the spinner background in Edit Manga Info
• Improve manga's backdrop color