Remove unexpected markup from documents

Some of the documents contain markup that HotDoc uses differently, or for
which we have a better alternative. Start change the usages found so far.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/developer/appdev-hello-world.md

@@ -54,8 +54,6 @@ To uninstall the code examples via Eclipse follow the below steps:
   * Right click on the project which you want to uninstall and select Uninstall (Native).
   ![](/images/image11.png)
 
-```
-
 ### Next
 
 |-|

content/developer/sdk-usage.md

@@ -24,8 +24,6 @@ Eclipse is the IDE used for application development in the SDK. Eclipse includes
 ![](/images/overview-docs.png)
 DevHelp is the standard browser for offline API documentation across many Open Source projects. The DevHelp installation in the SDK provides a local, offline version of the all the documentation found in the Application Developer Portal, including the Apertis API references.
 
-```
-
 # Persistent workspace
 
 The use of persistent workspace is optional. Check if you need persistent workspace before following these steps.
@@ -38,9 +36,13 @@ The SDK is distributed as VirtualBox images, and there is one VirtualBox image f
 
 See the [design](https://designs.apertis.org/private/latest/maintaining-workspace-across-sdk-updates.html) notes for background information and [README](https://gitlab.apertis.org/apertis/psdk/blob/master/README.md) for the complete documentation of psdk.
 
-> **WARNING**: It is recommended to make a backup copy of your SDK before continuing.
+{{% notice warning %}}
+It is recommended to make a backup copy of your SDK before continuing.
+{{% /notice %}}
 
-> **WARNING**: Configure the persistent disk on the **new** SDK before adding or changing files on the **new** SDK. Changes made to /home/user, /opt, and to /etc/cntlm.conf before configuring the persistent disk will be overwritten by the persistent disk. See the [README](https://gitlab.apertis.org/apertis/psdk/tree/apertis/v2020dev0#where-are-the-old-files-and-folders) for more details.
+{{% notice warning %}}
+Configure the persistent disk on the **new** SDK before adding or changing files on the **new** SDK. Changes made to /home/user, /opt, and to /etc/cntlm.conf before configuring the persistent disk will be overwritten by the persistent disk. See the [README](https://gitlab.apertis.org/apertis/psdk/tree/apertis/v2020dev0#where-are-the-old-files-and-folders) for more details.
+{{% /notice %}}
 
 ## Upgrading to a new SDK using a persistent disk
 
@@ -105,8 +107,6 @@ psdk will open in interactive mode, and will guide you trough the processes of c
 This will be much faster than initializing the disk. After psdk is done, it will ask you to reboot the SDK. Click OK, and wait for the reboot to complete.
 ![](/images/psdk-conf-success.png)
 
-```
-
 Congratulations!  You now have everything you need to start developing applications for Apertis.
 
 ### Next