Added proposals phase attributes to legislation processes form

Also added them to the list of accepted params and completed translations.

config/locales/en/admin.yml

@@ -258,6 +258,7 @@ en:
           process: Process
           debate_phase: Debate phase
           allegations_phase: Allegations phase
+          proposals_phase: Proposals phase
           start: Start
           end: End
           use_markdown: Use Markdown to format the text

config/locales/es/admin.yml

@@ -258,6 +258,7 @@ es:
           process: Proceso
           debate_phase: Fase previa
           allegations_phase: Fase de alegaciones
+          proposals_phase: Fase de propuestas
           start: Inicio
           end: Fin
           use_markdown: Usa Markdown para formatear el texto