added string extentions for email and passwords

app/src/main/java/be/ugent/sel/studeez/common/ext/StringExt.kt

@@ -0,0 +1,25 @@
+package be.ugent.sel.studeez.common.ext
+
+import android.util.Patterns
+import java.util.regex.Pattern
+
+private const val MIN_PASS_LENGTH = 6
+private const val PASS_PATTERN = "^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=\\S+$).{4,}$"
+
+fun String.isValidEmail(): Boolean {
+    return this.isNotBlank() && Patterns.EMAIL_ADDRESS.matcher(this).matches()
+}
+
+fun String.isValidPassword(): Boolean {
+    return this.isNotBlank() &&
+            this.length >= MIN_PASS_LENGTH &&
+            Pattern.compile(PASS_PATTERN).matcher(this).matches()
+}
+
+fun String.passwordMatches(repeated: String): Boolean {
+    return this == repeated
+}
+
+fun String.idFromParameter(): String {
+    return this.substring(1, this.length - 1)
+}