Context is lost the second time in Abecedarium activity

[llaske]

Step to reproduce:

• Open a new instance of Abecedarium activity
• Click on the book item, then on any letter
• Change the current language by clicking on the flag
• Close the activity
• Reopen the activity: it's open on the previous screen
• Close the activity again
• Reopen the activity: it's now open on the home screen
  The user expect to reopen the activity in the same context than when he leave it. Currently it's the case on first reopen but not the second time.

[llaske]

Fixed in #366

[llaske]

Closed in dd3c58d