feat(Matte): add Matte theme

Matte/README.md

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+# Matte
+
+## Screenshots
+
+![Queue Page](screenshots/queue.png)
+![Search Page](screenshots/search.png)
+![Customized Config](screenshots/customized.png)
+
+## More
+
+### Description
+Has a neat color pallete and a much cleaner interface
+
+### Notes
+Check the very top of `user.css` for quick configs
+
+For Windows users, here's how to make the window controls' background match with the topbar background:  
+Put this snippet into your `user.css`
+```css
+/* window controls background */
+.Root__top-bar {
+    background-image: linear-gradient(#4a5b6b, #4a5b6b); /* depends on the color */
+    background-repeat: no-repeat;
+    background-position: top right;
+    background-size: 135px 31px; /* depends on the set page zoom - this value is for 100% */
+}
+```
+![Window Controls](screenshots/winctrl.png)
+
+### Credits
+Based on [Matte by KDr3w](https://www.deviantart.com/kdr3w/art/Matte-758699852)  
+Created by [darkthemer](https://github.com/darkthemer)

Matte/color.ini

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+;COLORS KEYS DESCRIPTION
+; text               = Main text, playlist names in main field, name of playlist selected in sidebar, headings
+; subtext            = Text in main buttons in sidebar, playlist names in sidebar, artist names, mini infos, seekbar and volume bar background
+; topbar             = Topbar background
+; main               = Main field background
+; sidebar            = Sidebar background
+; player             = Player background
+; card               = Card and selected song background on hover
+; shadow             = Card and context menu drop shadow
+; selected-row       = Caption and playlist details, download and options buttons
+; button             = Accent color
+; button-active      = Accent color on select and hover
+; button-disabled    = Scrollbar color, tab background on hover, off toggle background
+; tab-active         = Tabbar active item background in header
+; notification       = Notification toast
+; notification-error = Notification error toast
+; misc               = Miscellaneous
+
+[matte]
+text               = FFFFFF
+subtext            = 7e8596
+topbar             = 232b32
+main               = 1c2228
+sidebar            = 181e23
+player             = 141b1f
+card               = 232d35
+shadow             = 000000
+selected-row       = 7e8596
+button             = 01BFA5
+button-active      = 01BFA5
+button-disabled    = 39454f
+tab-active         = 1c2228
+notification       = 1c2228
+notification-error = e22134
+misc               = 39454f