Implement template placeholders for Contentful

[kkartunov]

Add support for template placeholders. It will be using https://lodash.com/docs/4.17.15#template

Adding something like this in Contentful should result to rendered page when the user is logged in.

Hello __<%= profile.firstName %> <%= profile.lastName %>__(<%= profile.handle %>)!

Some data we have for you:
- userId: <%= profile.userId %>
- Autogenerated link to profile: <a href="https://topcoder.com/members/<%= profile.handle %>"><%= profile.handle %></a>

Test URL: https://community-app.topcoder-dev.com/examples/contentful/contentblock/2JEvQENG9pSUTdZSSAAxOK

[SathyaJayabal]

verified on dev