gitlab: Add issue templates

This adds two GitLab issue templates for:
* Epics
* Features

The actual templates are inspired by the ones Geary provides.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/763

.gitlab/issue_templates/Bug.md

@@ -0,0 +1,55 @@
+<!-- 
+Please read https://wiki.gnome.org/Community/GettingInTouch/BugReportingGuidelines
+first to ensure that you create a clear and specific issue.
+-->
+
+### Affected version
+
+<!--
+Provide at least the following information:
+* Your OS and version
+* Affected GNOME Shell version
+* Does this issue appear in XOrg and/or Wayland
+-->
+
+### Bug summary
+
+<!-- 
+Provide a short summary of the bug you encountered.
+-->
+
+### Steps to reproduce
+
+<!-- 
+1. Step one
+2. Step two
+3. ...
+-->
+
+### What happened
+
+<!-- 
+What did GNOME Shell do that was unexpected?
+-->
+
+### What did you expect to happen
+
+<!-- 
+What did you expect GNOME Shell to do?
+-->
+
+### Relevant logs, screenshots, screencasts etc.
+
+<!-- 
+If you have further information, such as technical documentation, logs,
+screenshots or screencasts related, please provide them here.
+
+If the bug is a crash, please obtain a stack trace with installed debug
+symbols (at least for GNOME Shell and Mutter) and attach it to
+this issue following the instructions on
+https://wiki.gnome.org/Community/GettingInTouch/Bugzilla/GettingTraces.
+-->
+
+
+<!-- Do not remove the following line. -->
+/label ~"1. Bug"

.gitlab/issue_templates/Feature.md

@@ -0,0 +1,30 @@
+<!-- 
+Please read https://wiki.gnome.org/Community/GettingInTouch/BugReportingGuidelines
+first to ensure that you create a clear and specific issue.
+-->
+
+### Feature summary
+
+<!-- 
+Describe what you would like to be able to do with GNOME Shell
+that you currently cannot do.
+-->
+
+### How would you like it to work
+
+<!-- 
+If you can think of a way GNOME Shell might be able to do this,
+let us know here.
+-->
+
+### Relevant links, screenshots, screencasts etc.
+
+<!-- 
+If you have further information, such as technical documentation,
+code, mockups or a similar feature in another desktop environments,
+please provide them here.
+-->
+
+
+<!-- Do not remove the following line. -->
+/label ~"1. Feature"