Restructure project directories (#333)

`/client/web` -> `/frontend`
`/client/cli` -> *delete for now*
`/client/native` -> *delete for now*
`/core/editor` -> `/editor`
`/core/document` -> `/graphene`
`/core/renderer` -> `/charcoal`
`/core/proc-macro` -> `/proc-macros` *(now plural)*

frontend/assets/16px-solid/eye-hidden.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
+	<path d="M8,4c3.5,0,5.9,2.8,6.8,4c-0.9,1.2-3.3,4-6.8,4S2.1,9.2,1.2,8C2.1,6.8,4.5,4,8,4 M8,3C3,3,0,8,0,8s3,5,8,5s8-5,8-5S13,3,8,3L8,3z" />
+</svg>