Feature/dynamic content (#605)

* Added dynamic content options

* Added defaults

* Added sane defaults

* Added IG operation providers for run time installation of IG's

* Refactored conditions for enabling the provider

* Refactoring

* Disable it by default in config as well

* document package install feature

* Added hosting options

* Provided better custom defaults

* Removed double default files

---------

Co-authored-by: Jose Costa Teixeira <jose.a.teixeira@gmail.com>

custom/about.html

@@ -0,0 +1,14 @@
+<p>
+    <b>This is a custom about page! It means you have configured 'custom_content_path: ./custom' in the application.yaml</b>
+</p>
+<p>
+    This server provides a complete implementation of the FHIR Specification
+    using a 100% open source software stack.
+</p>
+<p>
+    This server is built
+    from a number of modules of the
+    <a href="https://github.com/hapifhir/hapi-fhir/">HAPI FHIR</a>
+    project, which is a 100% open-source (Apache 2.0 Licensed) Java based
+    implementation of the FHIR specification.
+</p>

custom/welcome.html

@@ -0,0 +1,14 @@
+<p>
+    <b>This is a custom welcome page! It means you have configured 'custom_content_path: ./custom' in the application.yaml</b>
+</p>
+<p>
+    This server provides a complete implementation of the FHIR Specification
+    using a 100% open source software stack.
+</p>
+<p>
+    This server is built
+    from a number of modules of the
+    <a href="https://github.com/hapifhir/hapi-fhir/">HAPI FHIR</a>
+    project, which is a 100% open-source (Apache 2.0 Licensed) Java based
+    implementation of the FHIR specification.
+</p>