Change donations to contrbutions, add tabbed nav

Introduces components for tabbed navigation and adds a tab menu and item
for non-financial contributions to the donations/contributions page.

app/views/contributions/donations/index.html.erb

@@ -1,6 +1,6 @@
-<%= render HeaderComponent.new(title: "Donations") %>
+<%= render HeaderComponent.new(title: "Contributions") %>
 
-<%= render MainSimpleComponent.new do %>
+<%= render MainWithTabnavComponent.new(tabnav_partial: "shared/tabnav_contributions") do %>
   <section>
     <p class="mb-12">
       Your financial contributions to the development and upkeep of Kosmos
@@ -34,7 +34,9 @@
       </ul>
     <% else %>
       <p class="text-gray-500">
-        No donations to show.
+        The donation process is not automated yet. Please
+        <a href="https://wiki.kosmos.org/Main_Page#Community_.2F_Getting_in_touch_.2F_Getting_involved" class="ks-text-link" target="_blank">contact us</a>
+        if you'd like to contribute this way right now.
       </p>
     <% end %>
   </section>

app/views/contributions/projects/index.html.erb

@@ -0,0 +1,16 @@
+<%= render HeaderComponent.new(title: "Contributions") %>
+
+<%= render MainWithTabnavComponent.new(tabnav_partial: "shared/tabnav_contributions") do %>
+  <section>
+    <p class="mb-8">
+      Project contributions are how we develop and run all Kosmos software and
+      services. Everything we create and provide is free and open-source
+      software, even the page you're looking at right now!
+    </p>
+    <p>
+      Soon you will find a summary of your contributions here. Until then,
+      please refer to the
+      <a href="https://kredits.kosmos.org/" class="ks-text-link" target="_blank">Kredits dashboard</a>.
+    </p>
+  </section>
+<% end %>

app/views/donations/index.json.jbuilder

@@ -1 +0,0 @@
-json.array! @donations, partial: "donations/donation", as: :donation

app/views/shared/_main_nav.html.erb

@@ -1,9 +1,9 @@
 <%= link_to "Services", root_path,
       class: main_nav_class(@current_section, :dashboard) %>
+<%= link_to "Contributions", contributions_donations_path,
+      class: main_nav_class(@current_section, :contributions) %>
 <%= link_to "Invitations", invitations_path,
       class: main_nav_class(@current_section, :invitations) %>
-<%= link_to "Donations", donations_path,
-      class: main_nav_class(@current_section, :contributions) %>
 <%= link_to "Wallet", wallet_path,
       class: main_nav_class(@current_section, :wallet) %>
 <%= link_to "Settings", security_path,

app/views/shared/_tabnav_contributions.html.erb

@@ -0,0 +1,8 @@
+<%= render TabnavLinkComponent.new(
+  name: "Donations", path: contributions_donations_path,
+  active: current_page?(contributions_donations_path)
+) %>
+<%= render TabnavLinkComponent.new(
+  name: "Projects", path: contributions_projects_path,
+  active: current_page?(contributions_projects_path)
+) %>