The mainly changed:
1. Will not insert invalid apn data to database.
2. Clicking back button will save the APN data to database if the data is valid.
Test: make ROBOTEST_FILTER=ApnEditorTest -j40 RunSettingsRoboTests
Bug: 73745458
Bug: 67327863
Merged-In: Ie2c147cae03ad78d43c351e05add761b2dffac0c
Change-Id: Ie2c147cae03ad78d43c351e05add761b2dffac0c
(cherry picked from commit f39ef85653)
This add a data structure to store the apn data locally.
Test: unit test
Bug: 73745458
Bug: 67327863
Merged-In: Iae56583ab1c99f57154461c71a10b74db87ab1bd
Change-Id: Iae56583ab1c99f57154461c71a10b74db87ab1bd
(cherry picked from commit ee25956f57)