Refactoring I.

- Revamp whole DB to Display flow
- Filter Pipeline, arbitrary filtering and sorting
- Binary tree arrays for faster lookup & manipulation
- DB: introducing custom functions
- DB scheme: split req into heap & cache
- cache written by GlassVPN only
- heap written by Main App only
- Introducing DB separation: DBCore, DBCommon, DBAppOnly
- Introducing DB data sources: TestDataSource, GroupedDomainDataSource, RecordingsDB, DomainFilter
- Background sync: Move entries from cache to heap and notify all observers
- GlassVPN: Binary tree filter lookup
- GlassVPN: Reusing prepared statement

main/DB/DBExtensions.swift

@@ -0,0 +1,40 @@
+import UIKit
+
+extension GroupedDomain {
+	/// Return new `GroupedDomain` by adding `total` and `blocked` counts. Set `lastModified` to the maximum of the two.
+	static func +(a: GroupedDomain, b: GroupedDomain) -> Self {
+		GroupedDomain(domain: a.domain, total: a.total + b.total, blocked: a.blocked + b.blocked,
+					  lastModified: max(a.lastModified, b.lastModified), options: a.options ?? b.options )
+	}
+	/// Return new `GroupedDomain` by subtracting `total` and `blocked` counts.
+	static func -(a: GroupedDomain, b: GroupedDomain) -> Self {
+		GroupedDomain(domain: a.domain, total: a.total - b.total, blocked: a.blocked - b.blocked,
+					  lastModified: a.lastModified, options: a.options )
+	}
+}
+
+extension GroupedDomain {
+	var detailCellText: String { get {
+		return blocked > 0
+		? "\(lastModified.asDateTime())   —   \(blocked)/\(total) blocked"
+		: "\(lastModified.asDateTime())   —   \(total)"
+		}
+	}
+}
+
+extension FilterOptions {
+	func tableRowImage() -> UIImage? {
+		let blocked = contains(.blocked)
+		let ignored = contains(.ignored)
+		if blocked { return UIImage(named: ignored ? "block_ignore" : "shield-x") }
+		if ignored { return UIImage(named: "quicklook-not") }
+		return nil
+	}
+}
+
+extension Recording {
+	var fallbackTitle: String { get { "Unnamed Recording #\(id)" } }
+	var duration: Timestamp? { get { stop == nil ? nil : stop! - start } }
+	var durationString: String? { get { stop == nil ? nil : TimeFormat.from(duration!) } }
+}
+