Adding an default issue template

MR !461

.gitlab/issue_templates/Default.md

+<!-- Please drop all sections which are not relevant for your concrete use-case -->
+<!-- For enhancements and new features only the section 'Version information' might be relevant -->
+
+## Version information
+<!-- Which version of this software are you using? -->
+<!-- Which distribution are you using? -->
+
+## Steps to reproduce
+<!-- Please, explain as detailed as possible the sequence of actions necessary to reproduce the issue -->
+
+ 1. ...
+ 2. ...
+ 3. ...
+
+## Current behavior
+<!-- Please describe the current behaviour -->
+
+## Expected outcome
+<!-- Please describe the expected outcome -->
+
+## Backtrace
+<!--
+For crashes, it's best to get a backtrace to see which method failed to execute.
+
+To get a meaningful backtrace, you will need to install debug symbols. Check the Xfce wiki to see how to do so:
+https://docs.xfce.org/contribute/bugs/start#backtraces
+
+It's basically `ulimit -c unlimited` to produce coredumps on crashes and then using gdb on it to get the backtrace out of the coredump.
+-->
+
+## Additional information
+<!--
+ - Screenshots are useful for visual errors
+ - Please report any warning or message printed on the terminal
+-->
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