Added GPS information and 

Main Changes 
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- introduced GPS information
- introduced some of the missing connections between the preferences and the actual code
- modified the way data is uploaded to the server:
     1. long/lat and time are not associated to every single reading. This is a waste of data upload. Data is compacted into a list containing all the variables and which is uploaded in one go with a common  time/lat/long.
     2. taken care of cases where the server is not responding: created a local database where data is temporarily stored. Data will be sent next time the app is loaded
- the interface does not have a table with all data but a textview with only the current data: this is much easier to read
- the font color has been changed to greyish to white (I could not read it)
- the names of the views in the interface have now a positional name (row1_column2). This is because in the future it would be great to have the allocation of data flexible (so that you can change what is displayed where
- other minor changes

Issues
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The data displayed is wrong. This is not an issue with this branch. It is something that happens also in the original repository.
Not sure why this info would appear in README.md...