Implement Cobra CLI tooling, Viper config tooling (#336)

* start pulling out + replacing urfave and config

* replace many many instances of config

* move more stuff => viper

* properly remove urfave

* move some flags to root command

* add testrig commands to root

* alias config file keys

* start adding cli parsing tests

* reorder viper init

* remove config path alias

* fmt

* change config file keys to non-nested

* we're more or less in business now

* tidy up the common func

* go fmt

* get tests passing again

* add note about the cliparsing tests

* reorganize

* update docs with changes

* structure cmd dir better

* rename + move some files around

* fix dangling comma

docs/configuration/web.md

@@ -0,0 +1,21 @@
+# Web
+
+## Settings
+
+```yaml
+######################
+##### WEB CONFIG #####
+######################
+
+# Config pertaining to templating and serving of web pages/email notifications and the like
+
+# String. Directory from which gotosocial will attempt to load html templates (.tmpl files).
+# Examples: ["/some/absolute/path/", "./relative/path/", "../../some/weird/path/"]
+# Default: "./web/template/"
+web-template-base-dir: "./web/template/"
+
+# String. Directory from which gotosocial will attempt to serve static web assets (images, scripts).
+# Examples: ["/some/absolute/path/", "./relative/path/", "../../some/weird/path/"]
+# Default: "./web/assets/"
+web-asset-base-dir: "./web/assets/"
+```