Move server-selector over to path.join(), fix issues with cache swapping

Before, swapping would continually fail if a cache tried to be stored at a directory that already existed. The skipping mechanism likely also didn't work as intended. Both have been fixed now.
Additionally:
* Added .editorconfig file 
* Ran prettier format
* Misc. refactoring

.editorconfig

@@ -0,0 +1,19 @@
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+# 4 space indentation
+[*.js, *.css, *.html, *.json]
+indent_style = space
+indent_size = 4
+
+# Don't enforce anything in vendored code
+[*.min.*]
+end_of_line = unset
+insert_final_newline = unset
+indent_style = unset
+indent_style = unset