Use normal font size in search bar

Also update placeholder copy to be consistent with Android.

// FREEBIE

_locales/en/messages.json

@@ -60,7 +60,7 @@
       "description": "Menu item and header text for debug log modal, title case."
     },
     "searchForPeopleOrGroups": {
-      "message": "Search for people or groups",
+      "message": "Search...",
       "description": "Placeholder text in the search input"
     },
     "welcomeToSignal": {

stylesheets/_index.scss

@@ -89,6 +89,7 @@ input.search {
   padding: 10px;
   border: solid 1px $grey_l;
   outline-offset: -2px;
+  font-size: inherit;
 
   &.active {
     outline: solid 1px $blue;

stylesheets/manifest.css

@@ -500,7 +500,8 @@ input.search {
   width: 100%;
   padding: 10px;
   border: solid 1px #f3f3f3;
-  outline-offset: -2px; }
+  outline-offset: -2px;
+  font-size: inherit; }
   input.search.active {
     outline: solid 1px #2090ea; }
   input.search::-webkit-search-cancel-button {