Some localisation fixed related to data plans

[buttercookie42]

The whole handling of localised date and time strings in the code would probably merit a more thorough once over, but these commits fix at least the most glaring things I've immediately noticed.

Namely mainly

• re-using the strings for 'Weekly', 'Monthly' and 'Custom' from the settings panel for the text in the home activity produces ungrammatical results in some languages
• the validity text always uses English number ordinals (1st, 2nd and so on), plus month names based on the device language instead of the app language

[itsdrnoob]

Appreciate the initiative to make localisation better for Data Monitor. I've reviewed the changes, and overall it looks good. Proceeding with the merge.