Merge pull request #11881 from yashodha/CRM-21854

CRM-21854 - Contribution start date and end dates are not respected

diff --cc CRM/Contribute/Form/ContributionBase.php
Simple merge

diff --cc CRM/Contribute/Form/ContributionPage.php
Simple merge

diff --cc CRM/Contribute/Form/ContributionPage/Settings.php
Simple merge

diff --cc templates/CRM/Contribute/Form/ContributionPage/Settings.tpl
Simple merge