Fix the sales bugs reported in issues

[ureshiiYing]

The following has been fixed and updated:

• Sales Rank and Sales List command has been merged into one feature - now Sales List will show a ranked list instead.
• Added a cap to the maximum amount that sales update command can set (9,999,999)
• Update the UG to match these changes
• Added instructions to the examples in the UG sales commands

[codecov-io]

Codecov Report

Merging #235 (38688f8) into master (2771ca0) will increase coverage by 0.22%.
The diff coverage is 94.11%.

@@             Coverage Diff              @@
##             master     #235      +/-   ##
============================================
+ Coverage     66.42%   66.65%   +0.22%     
- Complexity      736      738       +2     
============================================
  Files           125      124       -1     
  Lines          2487     2498      +11     
  Branches        312      315       +3     
============================================
+ Hits           1652     1665      +13     
+ Misses          713      710       -3     
- Partials        122      123       +1     

Impacted Files	Coverage Δ	Complexity Δ
.../seedu/address/logic/parser/AddressBookParser.java	61.76% <ø> (-1.10%)	17.00 <0.00> (-1.00)
src/main/java/seedu/address/model/Drink.java	90.47% <ø> (ø)	8.00 <0.00> (ø)
...in/java/seedu/address/commons/util/StringUtil.java	93.10% <80.00%> (-2.73%)	11.00 <1.00> (+1.00)	⬇️
...seedu/address/logic/commands/SalesListCommand.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)
...edu/address/logic/commands/SalesUpdateCommand.java	100.00% <100.00%> (ø)	6.00 <0.00> (ø)
...in/java/seedu/address/logic/parser/ParserUtil.java	77.77% <100.00%> (+0.72%)	20.00 <0.00> (+1.00)
...address/logic/parser/SalesUpdateCommandParser.java	82.35% <100.00%> (+2.35%)	7.00 <0.00> (+1.00)
src/main/java/seedu/address/model/SalesBook.java	91.30% <100.00%> (ø)	21.00 <0.00> (ø)
...ava/seedu/address/model/UniqueSalesRecordList.java	92.30% <100.00%> (+0.37%)	30.00 <1.00> (+1.00)
...rc/main/java/seedu/address/model/ModelManager.java	84.44% <0.00%> (+3.33%)	37.00% <0.00%> (+1.00%)

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[WM71811]

LGTM

[WM71811]

LGTM

[yanbingtao]

LGTM