Added plaintext programming-lang option

... also bumped minimum importer version to 3.0.0

core/migrations/0020_auto_20190831_1417.py

+# Generated by Django 2.1.11 on 2019-08-31 14:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0019_merge_20190814_1437'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='submissiontype',
+            name='programming_language',
+            field=models.CharField(choices=[('c', 'C syntax highlighting'), ('java', 'Java syntax highlighting'), ('mipsasm', 'Mips syntax highlighting'), ('haskell', 'Haskell syntax highlighting'), ('plaintext', 'No syntax highlighting')], default='c', max_length=25),
+        ),
+    ]

core/models/submission_type.py

@@ -35,12 +35,14 @@ class SubmissionType(models.Model):
     JAVA = 'java'
     MIPS = 'mipsasm'
     HASKELL = 'haskell'
+    TEXT = 'plaintext'
 
     LANGUAGE_CHOICES = (
         (C, 'C syntax highlighting'),
         (JAVA, 'Java syntax highlighting'),
         (MIPS, 'Mips syntax highlighting'),
         (HASKELL, 'Haskell syntax highlighting'),
+        (TEXT, 'No syntax highlighting')
     )
 
     submission_type_id = models.UUIDField(primary_key=True,

util/importer.py

@@ -28,8 +28,8 @@ PASSWORDS = '.importer_passwords'
 YES = 'Y/n'
 NO = 'y/N'
 
-RUSTY_HEKTOR_MIN_VER = ">=1.0.0"
-RUSTY_HEKTOR_MAX_VER = "<2.0.0"
+RUSTY_HEKTOR_MIN_VER = ">=3.0.0"
+RUSTY_HEKTOR_MAX_VER = "<4.0.0"
 
 valid = {"yes": True, "y": True, "ye": True, "no": False, "n": False}