Open EarthRanger mobile db

[doneill]

Open and list tables in an EarthRanger mobile database

Test:

• Build and run the app
• Provide path to exported er database
• Confirm db can open

# command
er open earthranger.db

# response
earthranger.db successfully opened

• list db tables

# command
er open earthranger.db -t

# response
accounts_user
sqlite_sequence
user_profiles
user_subjects
event_type
event_category
events
attachments
sync_states
patrol_types
patrols
patrol_segments