Added a issue report template (#779)

.github/ISSUE_TEMPLATE.md

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+Before submitting an issue please make sure you tick and agree all the following check boxes:
+
+- [ ] Checked the current issues database and no similar issue was already discussed
+- [ ] Ran any database upgrade scripts (e.g. database/2.4_to_3.0.sql)
+- [ ] Read the README, WHATS_NEW and UPGRADE
+- [ ] Read the FAQ (https://github.com/jekkos/opensourcepos#faq) for any known install and/or upgrade gotchas
+- [ ] I'm reporting an issue of an unmodified OSPOS installation
+- [ ] The PHP version I use is at least 5.5 and not 7.x
+- [ ] I know the version of OSPOS and git commit hash (check the footer of your OSPOS) and will add to my issue report
+- [ ] I know the name and version of OS, Web server and MySQL and will add to my issue report
+- [ ] I know the step to reproduce the issue and will add to my issue report