Launch task directly into split terminal

Issue Type: <b>Feature Request</b> The integrated terminal split panes should support launching a task from the command palette into a split terminal panel. Here is the current workflow 1. Launch a long-running task from command palette by typing `ctrl+p -> task first-watcher-task -> enter`. (A new terminal window appears, running the task). 2. Click the split terminal button to create a split terminal. 3. In the split terminal, type the arguments for the second task and run it by pressing the enter key in the terminal. Can't run `ctrl+p -> task second-watcher-task -> enter` because that would open a whole new terminal section of its own. Here is the desired workflow 1. Launch a long-running task from command palette by typing `ctrl+p -> task some-watcher-task -> enter`. (A new terminal window appears, running the task). 2. Launch the second long-running task from comand palette by typing `ctrl+p -> task second-watcher-task -> enter`. Somehow, this task runs in a second panel of the split terminal, based on some extra command, a task configuration setting, or perhaps by having focus in an already opened split terminal. VS Code version: Code - Insiders 1.22.0-insider (81335051b2d1460112905c2bce23c205e7cdd231, 2018-04-03T01:09:54.914Z) OS version: Windows_NT x64 6.1.7601 <!-- generated by issue reporter -->