Fix system overview edit hostname form validation

- Add pattern for no spaces
- Fix character count
- Prepopulate hostname in input field
- Show error for invalid input
- Improve form accessibility
- Correct global disabled primary button style

Resolves openbmc/phosphor-webui#71

Signed-off-by: Dixsie Wolmers <dixsiew@gmail.com>
Change-Id: Ia0601ac7c52229d0606dc5b13397b468fa81426d
diff --git a/app/overview/styles/system-overview.scss b/app/overview/styles/system-overview.scss
index 01b7bc9..6bef6ed 100644
--- a/app/overview/styles/system-overview.scss
+++ b/app/overview/styles/system-overview.scss
@@ -46,8 +46,12 @@
   margin-bottom: 0;
 }
 
-.modal__char-count {
-  text-align: right;
+.modal__char-count,
+.modal__error {
   font-size: .8em;
   color: $darkgrey;
 }
+
+.modal__error {
+  color: $error-color;
+}
\ No newline at end of file