added alert dialog, search by price, added location choose feature, Used LH theme

Closes #13 (closed), #17 (closed), #18 (closed), #19 (closed), #20 (closed), #25 (closed), #26 (closed) ,#29 (closed) ,#28 (closed) ,#27 (closed)

• Added Unit tests
• completed readme.md
• Fixed dart analysis
• added license
• fixed bugs
• Worked on share,about screens of app
• Search by price
• unit tests passed
• Splash screen created
• Used LH colors for theme
• Created table in readme.md for screenshots of App
• Added intro slides in App

Choose a state feature

If permission is denied forever then user has to manually allow from settings

A Dialog to show all states of US for location changing

Search by price feature: Enable it from Filter