Convert image URLs in React to require calls

This allows Webpack to insert the proper image URL after builds steps like
adding a hash and so on. The path you supply to `require` is relative to the JS
source file, just like any other would be.

src/components/views/rooms/Stickerpicker.js

@@ -152,7 +152,7 @@ export default class Stickerpicker extends React.Component {
                 className='mx_Stickers_contentPlaceholder'>
                 <p>{ _t("You don't currently have any stickerpacks enabled") }</p>
                 <p className='mx_Stickers_addLink'>{ _t("Add some now") }</p>
-                <img src='img/stickerpack-placeholder.png' alt="" />
+                <img src={require("../../../../res/img/stickerpack-placeholder.png")} alt="" />
             </AccessibleButton>
         );
     }
@@ -351,7 +351,7 @@ export default class Stickerpicker extends React.Component {
                     onClick={this._onHideStickersClick}
                     ref='target'
                     title={_t("Hide Stickers")}>
-                    <TintableSvg src="img/feather-icons/face.svg" width="20" height="20" />
+                    <TintableSvg src={require("../../../../res/img/feather-icons/face.svg")} width="20" height="20" />
                 </AccessibleButton>;
         } else {
             // Show show-stickers button
@@ -362,7 +362,7 @@ export default class Stickerpicker extends React.Component {
                     className="mx_MessageComposer_stickers"
                     onClick={this._onShowStickersClick}
                     title={_t("Show Stickers")}>
-                    <TintableSvg src="img/feather-icons/face.svg" width="20" height="20" />
+                    <TintableSvg src={require("../../../../res/img/feather-icons/face.svg")} width="20" height="20" />
                 </AccessibleButton>;
         }
         return <div>