Allow colorization of history messages

History was always printed with `THEME_DEFAULT` we now use
`THEME_TEXT_HISTORY` which is accesible in theme files via
`main.text.history`.

Fix https://github.com/profanity-im/profanity/issues/1170

src/config/theme.h

@@ -135,6 +135,7 @@ typedef enum {
     THEME_BLACK_BOLD,
     THEME_MAGENTA,
     THEME_MAGENTA_BOLD,
+    THEME_TEXT_HISTORY,
 } theme_item_t;
 
 void theme_init(const char *const theme_name);