Added JNI interface for filling spinner

Divecomputer list in the main activity needs to be filled with appropriate
vendors and products. This is done by natively calling libdivecomputer
functions.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
DcData class for storing divecomputer info

Rather than storing individual elements, we can store the information in an
object. This provides greater flexibility.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Made DcData constructor parcelable

So that the object can be passed between activities via intents.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>