A bit of code cleanup, README updates

[TacoTheDank]

1st commit

• Miscellaneous code cleanup

2nd commit

• Adjusted codestyle in res and manifest

3rd commit

• Get rid of old support cardview (I hope this is fine)
• Fix medicinal plant string typo
• Extract Search and Settings strings

4th commit

• Update badges (I had to manually fix the amazon badge to align properly with the other two)
• Fix some English
• Add link to field manual

[TacoTheDank]

@ligi Should be good now, I think