Update CHANGELOG.md
Merge pull request #112 from xLaMbChOpSx/master

Various bugfixes, improvements and updates
Update SOURCES
Added small clarifications
OpenCellID - User Specific API Key Support

Modifed the OpenCellID methods to only operate if an API Key has been
entered through the application settings, enabling each user to request
and use their own keys.

This will need to be extended once functionality has been confirmed to
provide more instruction to users regarding the registration process,
such as through alert dialogs and details regarding the OCID website etc.

Key is stored on the device and only used when initiating communication
with the OCID servers, as with all previous versions no personal
information is sent to OCID only necessary cell/location information as
required by their API methods.