Mer: Polish MerConnection a bit

Minor/cosmetic fixes prior to extending connection state machine.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Implement more reliable VM connection state management

[qtc] Mer: Implement more reliable VM connection state management. Relates MER#769 MER#814

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Do not lose VM connection state

Do not reuse single MerConnection instance. Create one MerConnection
instance for each virtual machine to keep connection state.

This also allows to use the MerConnection interface to control VMs also
with no Mer project open.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Handle VMs started outside of qtc more considerately

[qtc] Mer: Handle VMs started outside of qtc more considerately

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Do not interrupt build/deploy when VM is not started

- Handle SDK the same way as emulator - with a dedicated build step
- Wait for VM to start instead of aborting build/deploy

It also forces the "start VM" step is always present - not only
convenient but also important to not break projects with existing
.pro.user.

[qtc] Mer: Do not interrupt build/deploy when VM is not started

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Remove unused MerConnectionPrompt

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Report VM connection errors more conveniently

Do not use "Issues" pane to inform about VM connecting errors. This pane
is supposed to list build issues - which is not always the case. Use the
"General Messages" pane instead.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Allow to configure SSH timeout for SDK VM

[qtc] Mer: Allow to configure SSH timeout for SDK VM. Relates MER#814

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Use ICore::dialogParent() for all dialogs

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Allow to lock down VM connections

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Allow user to close VM before changing src path

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Close just-starting VMs on exit more reliably

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Remove (nearly) unused MerActionManager

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Fix layout in SDK details widget

Grid layout was used with only first row of the third column occupied,
and thus limiting horizontal space for following rows. Use form layout
with hbox inside instead.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Layout SDK options widget similarly to that one for devices

Basically place the buttons "Add", "Remove" and "Start Virtual Machine"
on the right side.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>