Feature Request: Custom Hike reminders.

**Is your feature request related to a problem? Please describe.**
Building up on #52, we can add custom reminders (msg and time). For eg using a TimePicker() user can select time to be reminded at, default being 1 hr before the hike. This can be extended to be used to add reminders before expiry date also.

**Are you working on this? (Yes/No)**
Yes