[Android] Share URL instead of description

Share detail URL, description is too long.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[Android] Remove unused import

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[Android] Add event data cache

Cache event json data on the system cache dir. Use cached data if cache
file exists and it's not older than two days, or if http connection fails.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>