Merge branch '30-submit-analysis-without-chemical-formula' into 'init19'

Resolve "Submit analysis without chemical formula"

Closes #30

See merge request !22

app/models/sample.rb

@@ -7,7 +7,7 @@ class Sample < ApplicationRecord
   belongs_to :user
   validates :user_id, presence: true
   validates :name, presence: true, length: { maximum: 50 }
-  validates :formula, presence: true, length: { maximum: 140 }
+  validates :formula, length: { maximum: 140 }
   validates :status, presence: true, length: { maximum: 140 }
   before_save :calculate_percentage