Feature/add summary command

[stanleytangzh]

closes #106
Create a new command called 'Summary'. It will give a summary of the application statuses of all candidates.

[codecov]

Codecov Report

Attention: Patch coverage is 36.61972% with 45 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main/java/seedu/address/ui/OverviewPanel.java	0.00%	23 Missing ⚠️
src/main/java/seedu/address/ui/MainWindowNew.java	0.00%	16 Missing ⚠️
...rc/main/java/seedu/address/ui/PersonListPanel.java	0.00%	5 Missing ⚠️
...a/seedu/address/logic/commands/SummaryCommand.java	94.11%	1 Missing ⚠️

Files with missing lines	Coverage Δ	Complexity Δ
...rc/main/java/seedu/address/logic/LogicManager.java	78.26% <100.00%> (+0.98%)	4.00 <1.00> (+1.00)
.../seedu/address/logic/parser/AddressBookParser.java	88.46% <100.00%> (+0.46%)	14.00 <0.00> (+1.00)
src/main/java/seedu/address/model/Model.java	100.00% <ø> (ø)	1.00 <0.00> (ø)
...rc/main/java/seedu/address/model/ModelManager.java	100.00% <100.00%> (ø)	26.00 <3.00> (+3.00)
...a/seedu/address/logic/commands/SummaryCommand.java	94.11% <94.11%> (ø)	5.00 <5.00> (?)
...rc/main/java/seedu/address/ui/PersonListPanel.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
src/main/java/seedu/address/ui/MainWindowNew.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
src/main/java/seedu/address/ui/OverviewPanel.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)