convert image mimetype to lowercase, remove unused imports/tags

app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt

@@ -13,7 +13,6 @@ import android.os.Handler
 import android.provider.Telephony
 import android.telephony.SubscriptionManager
 import android.text.TextUtils
-import android.util.Log
 import android.util.TypedValue
 import android.view.*
 import android.view.inputmethod.EditorInfo
@@ -55,7 +54,6 @@ import org.greenrobot.eventbus.ThreadMode
 class ThreadActivity : SimpleActivity() {
     private val MIN_DATE_TIME_DIFF_SECS = 300
     private val PICK_ATTACHMENT_INTENT = 1
-    private val TAG = "ThreadActivity"
 
     private var threadId = 0L
     private var currentSIMCardIndex = 0

app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/String.kt

@@ -12,5 +12,5 @@ fun String.getExtensionFromMimeType(): String {
 }
 
 fun String.isImageMimeType(): Boolean {
-    return startsWith("image")
+    return lowercase().startsWith("image")
 }