fx102: Cleans up scss files, removes shadow DOM use from CEs (#3051)

Removes a huge amount of excessive files and duplication for CE scss.
All CE css is now output in the single
zotero-react-client.css file.

Moving all CE styling into a single stylesheet required removing their
shadow DOMs. It is desirable anyway, since you want to
be able to style CEs from "outside", when embedding in different
contexts.

Shadow removal required some CE code changes to maintain
functionality.

Elements refactored:
- attachment-box (displayed when an attachment (like PDF) is selected in
the item tree)
- color-picker (in the tag color selector)
- guidance-panel (displayed on first run when editing authors for a book
section)
- item-box (info tab in the item pane)
- note-editor
- notes-box (note tab in the item pane)
- quick-search-textbox
- related-box (related tab in the item pane)
- tags-box (tags tab in the item pane)
- zoterosearch (advanced search condition builder form)

scss/linux/elements/_itemBox.scss

@@ -0,0 +1,20 @@
+item-box {
+	th {
+		margin-top: 1px;
+	}
+
+	.zotero-clicky {
+		min-height: 17px;
+	}
+
+	td input {
+		margin: -2px 0 0;
+		padding: 1px;
+		border-width: 1px;
+		border-radius: 6px;
+	}
+	
+	.creator-name-box input {
+		margin-bottom: -1px;
+	}
+}

scss/linux/elements/_quickSearchTextbox.scss

@@ -0,0 +1,10 @@
+#zotero-tb-search-menu-button {
+	list-style-image: none; /* Dropmarker added automatically on Linux */
+	-moz-appearance: toolbarbutton-dropdown !important;
+	width: 12px;
+	height: 12px;
+}
+
+#zotero-tb-search .textbox-search-icon {
+	visibility: hidden;
+}