Localize notification_utils to the API

This changeset pulls in all of the notification_utils code directly into the API and removes it as an external dependency.  We are doing this to cut down on operational maintenance of the project and will begin removing parts of it no longer needed for the API.

Signed-off-by: Carlo Costino <carlo.costino@gsa.gov>

notifications_utils/__init__.py

@@ -0,0 +1,25 @@
+import re
+
+SMS_CHAR_COUNT_LIMIT = 918  # 153 * 6, no network issues but check with providers before upping this further
+LETTER_MAX_PAGE_COUNT = 10
+DAILY_MESSAGE_LIMIT = 10000
+
+# regexes for use in recipients.validate_email_address.
+# Valid characters taken from https://en.wikipedia.org/wiki/Email_address#Local-part
+# Note: Normal apostrophe eg `Firstname-o'surname@domain.com` is allowed.
+# hostname_part regex: xn in regex signifies possible punycode conversions, which would start `xn--`;
+# the hyphens are matched for later in the regex.
+hostname_part = re.compile(r"^(xn|[a-z0-9]+)(-?-[a-z0-9]+)*$", re.IGNORECASE)
+tld_part = re.compile(r"^([a-z]{2,63}|xn--([a-z0-9]+-)*[a-z0-9]+)$", re.IGNORECASE)
+VALID_LOCAL_CHARS = r"a-zA-Z0-9.!#$%&'*+/=?^_`{|}~\-"
+EMAIL_REGEX_PATTERN = r"^[{}]+@([^.@][^@\s]+)$".format(VALID_LOCAL_CHARS)
+email_with_smart_quotes_regex = re.compile(
+    # matches wider than an email - everything between an at sign and the nearest whitespace
+    r"(^|\s)\S+@\S+(\s|$)",
+    flags=re.MULTILINE,
+)
+
+# The magic sequence is a ‘unique’ series of characters which we temporarily insert
+# and then later remove when performing tricky formatting operations
+MAGIC_SEQUENCE = "🇬🇧🐦✉️"
+magic_sequence_regex = re.compile(MAGIC_SEQUENCE)