Spelling in API and POS update

Corrected acknowledgementMode to acknowledgmentMode in API section.
Removed info about receipts, etc, under paragraph "Add SEQR as payment
in your POS - Start the payment by pressing the SEQR payment button in
POS" under POS section. Added info about
Added "Get terminal context"

Added first step "Get terminal context" in Basic SEQR payment, with
reference to example terminal ID and password.
Changed QR code image inr POS section
Update index.md

- mentioning credentials on the first payment page
Update index.md

- made it more clear that this is an example POS integration
Merge pull request #3 from SeamlessDistribution/master

Merge branch 'develop'