Updated login page to comply with Material standards

[theGeekyLad]

Login screen with Material Design

• Updated EditTexts with Material counterparts
• Included LinearLayout to wrap components and leverage weight property for handling spacing better (instead of margin and padding)
• Sanitized TextViews and Buttons in terms of style and size

Screenshots

activity_onboarding.xml fixes

• In the earlier PR, I limited the reg. fields to only allow numbers - updated that to support alphanumeric + all-caps characters

[theGeekyLad]

Hey @ugwulo , I tried a split PR but surprisingly commit fe7b8e8 got included with this one. Would really appreciate if you could add the topic hacktoberfest to this repository and, if you deem it valid, accept my PR with the label hacktoberfest-accepted! Also, do let me know if I should change anything.