Add new date format and 10-year period option (#154)

Added 'YYYYMMDD' to supported date formats in Family model.
Introduced a 'last_10_years' period option in Period model with appropriate labels and date range.

app/models/family.rb

@@ -10,7 +10,8 @@ class Family < ApplicationRecord
     [ "YYYY/MM/DD", "%Y/%m/%d" ],
     [ "MM/DD/YYYY", "%m/%d/%Y" ],
     [ "D/MM/YYYY", "%e/%m/%Y" ],
-    [ "YYYY.MM.DD", "%Y.%m.%d" ]
+    [ "YYYY.MM.DD", "%Y.%m.%d" ],
+    [ "YYYYMMDD", "%Y%m%d" ]
   ].freeze
 
   has_many :users, dependent: :destroy

app/models/period.rb

@@ -63,6 +63,12 @@ class Period
       label_short: "5Y",
       label: "Last 5 Years",
       comparison_label: "vs. 5 years ago"
+    },
+    "last_10_years" => {
+      date_range: -> { [ 10.years.ago.to_date, Date.current ] },
+      label_short: "10Y",
+      label: "Last 10 Years",
+      comparison_label: "vs. 10 years ago"
     }
   }