Avoid to fail to load `config-org' because of Plantuml

* config-plantuml.el: Setup `ob-plantuml' once `org-mode' has been
  loaded.
* config-org.el: Remove Plantuml's interaction with Org Babel.
* config-misc.el: Avoid checking the network here
Elpa Update
Use diary.org to store my diary

* config-org.el: Use diary.org to store my diary, especially with 'i'.
* config-org.el: Enable `org-magit' magit link within org-mode.
Switch to the new Org Mode exporter
Add useful bindings to C*-mode